2005-04-16 15:20:36 -07:00
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2009-01-06 03:04:54 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2007-10-19 22:38:44 +01:00
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2008-04-24 22:02:01 +01:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2009-01-06 03:05:15 +00:00
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2005-04-16 15:20:36 -07:00
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2006-06-26 00:27:35 -07:00
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2009-12-10 23:52:30 +00:00
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2008-07-21 12:00:32 +01:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:10 +00:00
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2009-04-02 19:55:34 +01:00
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2019-03-17 14:22:57 +02:00
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2009-04-02 19:55:34 +01:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:12 +00:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:35 +00:00
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2009-04-02 19:55:34 +01:00
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2015-06-21 16:31:33 -04:00
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2009-04-02 19:55:34 +01:00
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dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
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2018-08-07 16:56:00 -04:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
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2018-05-20 18:25:53 -04:00
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2010-03-06 02:32:33 +00:00
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2009-12-10 23:52:10 +00:00
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2009-04-02 19:55:34 +01:00
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2010-03-06 02:32:33 +00:00
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2009-04-02 19:55:34 +01:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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dm snapshot: Fix excessive memory usage and workqueue stalls
kcopyd has no upper limit to the number of jobs one can allocate and
issue. Under certain workloads this can lead to excessive memory usage
and workqueue stalls. For example, when creating multiple dm-snapshot
targets with a 4K chunk size and then writing to the origin through the
page cache. Syncing the page cache causes a large number of BIOs to be
issued to the dm-snapshot origin target, which itself issues an even
larger (because of the BIO splitting taking place) number of kcopyd
jobs.
Running the following test, from the device mapper test suite [1],
dmtest run --suite snapshot -n many_snapshots_of_same_volume_N
, with 8 active snapshots, results in the kcopyd job slab cache growing
to 10G. Depending on the available system RAM this can lead to the OOM
killer killing user processes:
[463.492878] kthreadd invoked oom-killer: gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP),
nodemask=(null), order=1, oom_score_adj=0
[463.492894] kthreadd cpuset=/ mems_allowed=0
[463.492948] CPU: 7 PID: 2 Comm: kthreadd Not tainted 4.19.0-rc7 #3
[463.492950] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[463.492952] Call Trace:
[463.492964] dump_stack+0x7d/0xbb
[463.492973] dump_header+0x6b/0x2fc
[463.492987] ? lockdep_hardirqs_on+0xee/0x190
[463.493012] oom_kill_process+0x302/0x370
[463.493021] out_of_memory+0x113/0x560
[463.493030] __alloc_pages_slowpath+0xf40/0x1020
[463.493055] __alloc_pages_nodemask+0x348/0x3c0
[463.493067] cache_grow_begin+0x81/0x8b0
[463.493072] ? cache_grow_begin+0x874/0x8b0
[463.493078] fallback_alloc+0x1e4/0x280
[463.493092] kmem_cache_alloc_node+0xd6/0x370
[463.493098] ? copy_process.part.31+0x1c5/0x20d0
[463.493105] copy_process.part.31+0x1c5/0x20d0
[463.493115] ? __lock_acquire+0x3cc/0x1550
[463.493121] ? __switch_to_asm+0x34/0x70
[463.493129] ? kthread_create_worker_on_cpu+0x70/0x70
[463.493135] ? finish_task_switch+0x90/0x280
[463.493165] _do_fork+0xe0/0x6d0
[463.493191] ? kthreadd+0x19f/0x220
[463.493233] kernel_thread+0x25/0x30
[463.493235] kthreadd+0x1bf/0x220
[463.493242] ? kthread_create_on_cpu+0x90/0x90
[463.493248] ret_from_fork+0x3a/0x50
[463.493279] Mem-Info:
[463.493285] active_anon:20631 inactive_anon:4831 isolated_anon:0
[463.493285] active_file:80216 inactive_file:80107 isolated_file:435
[463.493285] unevictable:0 dirty:51266 writeback:109372 unstable:0
[463.493285] slab_reclaimable:31191 slab_unreclaimable:3483521
[463.493285] mapped:526 shmem:4903 pagetables:1759 bounce:0
[463.493285] free:33623 free_pcp:2392 free_cma:0
...
[463.493489] Unreclaimable slab info:
[463.493513] Name Used Total
[463.493522] bio-6 1028KB 1028KB
[463.493525] bio-5 1028KB 1028KB
[463.493528] dm_snap_pending_exception 236783KB 243789KB
[463.493531] dm_exception 41KB 42KB
[463.493534] bio-4 1216KB 1216KB
[463.493537] bio-3 439396KB 439396KB
[463.493539] kcopyd_job 6973427KB 6973427KB
...
[463.494340] Out of memory: Kill process 1298 (ruby2.3) score 1 or sacrifice child
[463.494673] Killed process 1298 (ruby2.3) total-vm:435740kB, anon-rss:20180kB, file-rss:4kB, shmem-rss:0kB
[463.506437] oom_reaper: reaped process 1298 (ruby2.3), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
Moreover, issuing a large number of kcopyd jobs results in kcopyd
hogging the CPU, while processing them. As a result, processing of work
items, queued for execution on the same CPU as the currently running
kcopyd thread, is stalled for long periods of time, hurting performance.
Running the aforementioned test we get, in dmesg, messages like the
following:
[67501.194592] BUG: workqueue lockup - pool cpus=4 node=0 flags=0x0 nice=0 stuck for 27s!
[67501.195586] Showing busy workqueues and worker pools:
[67501.195591] workqueue events: flags=0x0
[67501.195597] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195611] pending: cache_reap
[67501.195641] workqueue mm_percpu_wq: flags=0x8
[67501.195645] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195656] pending: vmstat_update
[67501.195682] workqueue kblockd: flags=0x18
[67501.195687] pwq 5: cpus=2 node=0 flags=0x0 nice=-20 active=1/256
[67501.195698] pending: blk_timeout_work
[67501.195753] workqueue kcopyd: flags=0x8
[67501.195757] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195768] pending: do_work [dm_mod]
[67501.195802] workqueue kcopyd: flags=0x8
[67501.195806] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195817] pending: do_work [dm_mod]
[67501.195834] workqueue kcopyd: flags=0x8
[67501.195838] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195848] pending: do_work [dm_mod]
[67501.195881] workqueue kcopyd: flags=0x8
[67501.195885] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195896] pending: do_work [dm_mod]
[67501.195920] workqueue kcopyd: flags=0x8
[67501.195924] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=2/256
[67501.195935] in-flight: 67:do_work [dm_mod]
[67501.195945] pending: do_work [dm_mod]
[67501.195961] pool 8: cpus=4 node=0 flags=0x0 nice=0 hung=27s workers=3 idle: 129 23765
The root cause for these issues is the way dm-snapshot uses kcopyd. In
particular, the lack of an explicit or implicit limit to the maximum
number of in-flight COW jobs. The merging path is not affected because
it implicitly limits the in-flight kcopyd jobs to one.
Fix these issues by using a semaphore to limit the maximum number of
in-flight kcopyd jobs. We grab the semaphore before allocating a new
kcopyd job in start_copy() and start_full_bio() and release it after the
job finishes in copy_callback().
The initial semaphore value is configurable through a module parameter,
to allow fine tuning the maximum number of in-flight COW jobs. Setting
this parameter to zero initializes the semaphore to INT_MAX.
A default value of 2048 maximum in-flight kcopyd jobs was chosen. This
value was decided experimentally as a trade-off between memory
consumption, stalling the kernel's workqueues and maintaining a high
enough throughput.
Re-running the aforementioned test:
* Workqueue stalls are eliminated
* kcopyd's job slab cache uses a maximum of 130MB
* The time taken by the test to write to the snapshot-origin target is
reduced from 05m20.48s to 03m26.38s
[1] https://github.com/jthornber/device-mapper-test-suite
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-10-31 17:53:08 -04:00
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2009-04-02 19:55:34 +01:00
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2010-03-06 02:32:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:35 +00:00
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2019-06-19 17:05:54 -04:00
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2009-12-10 23:52:35 +00:00
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2009-12-10 23:52:33 +00:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:32 +00:00
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dm snapshot: Fix excessive memory usage and workqueue stalls
kcopyd has no upper limit to the number of jobs one can allocate and
issue. Under certain workloads this can lead to excessive memory usage
and workqueue stalls. For example, when creating multiple dm-snapshot
targets with a 4K chunk size and then writing to the origin through the
page cache. Syncing the page cache causes a large number of BIOs to be
issued to the dm-snapshot origin target, which itself issues an even
larger (because of the BIO splitting taking place) number of kcopyd
jobs.
Running the following test, from the device mapper test suite [1],
dmtest run --suite snapshot -n many_snapshots_of_same_volume_N
, with 8 active snapshots, results in the kcopyd job slab cache growing
to 10G. Depending on the available system RAM this can lead to the OOM
killer killing user processes:
[463.492878] kthreadd invoked oom-killer: gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP),
nodemask=(null), order=1, oom_score_adj=0
[463.492894] kthreadd cpuset=/ mems_allowed=0
[463.492948] CPU: 7 PID: 2 Comm: kthreadd Not tainted 4.19.0-rc7 #3
[463.492950] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[463.492952] Call Trace:
[463.492964] dump_stack+0x7d/0xbb
[463.492973] dump_header+0x6b/0x2fc
[463.492987] ? lockdep_hardirqs_on+0xee/0x190
[463.493012] oom_kill_process+0x302/0x370
[463.493021] out_of_memory+0x113/0x560
[463.493030] __alloc_pages_slowpath+0xf40/0x1020
[463.493055] __alloc_pages_nodemask+0x348/0x3c0
[463.493067] cache_grow_begin+0x81/0x8b0
[463.493072] ? cache_grow_begin+0x874/0x8b0
[463.493078] fallback_alloc+0x1e4/0x280
[463.493092] kmem_cache_alloc_node+0xd6/0x370
[463.493098] ? copy_process.part.31+0x1c5/0x20d0
[463.493105] copy_process.part.31+0x1c5/0x20d0
[463.493115] ? __lock_acquire+0x3cc/0x1550
[463.493121] ? __switch_to_asm+0x34/0x70
[463.493129] ? kthread_create_worker_on_cpu+0x70/0x70
[463.493135] ? finish_task_switch+0x90/0x280
[463.493165] _do_fork+0xe0/0x6d0
[463.493191] ? kthreadd+0x19f/0x220
[463.493233] kernel_thread+0x25/0x30
[463.493235] kthreadd+0x1bf/0x220
[463.493242] ? kthread_create_on_cpu+0x90/0x90
[463.493248] ret_from_fork+0x3a/0x50
[463.493279] Mem-Info:
[463.493285] active_anon:20631 inactive_anon:4831 isolated_anon:0
[463.493285] active_file:80216 inactive_file:80107 isolated_file:435
[463.493285] unevictable:0 dirty:51266 writeback:109372 unstable:0
[463.493285] slab_reclaimable:31191 slab_unreclaimable:3483521
[463.493285] mapped:526 shmem:4903 pagetables:1759 bounce:0
[463.493285] free:33623 free_pcp:2392 free_cma:0
...
[463.493489] Unreclaimable slab info:
[463.493513] Name Used Total
[463.493522] bio-6 1028KB 1028KB
[463.493525] bio-5 1028KB 1028KB
[463.493528] dm_snap_pending_exception 236783KB 243789KB
[463.493531] dm_exception 41KB 42KB
[463.493534] bio-4 1216KB 1216KB
[463.493537] bio-3 439396KB 439396KB
[463.493539] kcopyd_job 6973427KB 6973427KB
...
[463.494340] Out of memory: Kill process 1298 (ruby2.3) score 1 or sacrifice child
[463.494673] Killed process 1298 (ruby2.3) total-vm:435740kB, anon-rss:20180kB, file-rss:4kB, shmem-rss:0kB
[463.506437] oom_reaper: reaped process 1298 (ruby2.3), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
Moreover, issuing a large number of kcopyd jobs results in kcopyd
hogging the CPU, while processing them. As a result, processing of work
items, queued for execution on the same CPU as the currently running
kcopyd thread, is stalled for long periods of time, hurting performance.
Running the aforementioned test we get, in dmesg, messages like the
following:
[67501.194592] BUG: workqueue lockup - pool cpus=4 node=0 flags=0x0 nice=0 stuck for 27s!
[67501.195586] Showing busy workqueues and worker pools:
[67501.195591] workqueue events: flags=0x0
[67501.195597] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195611] pending: cache_reap
[67501.195641] workqueue mm_percpu_wq: flags=0x8
[67501.195645] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195656] pending: vmstat_update
[67501.195682] workqueue kblockd: flags=0x18
[67501.195687] pwq 5: cpus=2 node=0 flags=0x0 nice=-20 active=1/256
[67501.195698] pending: blk_timeout_work
[67501.195753] workqueue kcopyd: flags=0x8
[67501.195757] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195768] pending: do_work [dm_mod]
[67501.195802] workqueue kcopyd: flags=0x8
[67501.195806] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195817] pending: do_work [dm_mod]
[67501.195834] workqueue kcopyd: flags=0x8
[67501.195838] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195848] pending: do_work [dm_mod]
[67501.195881] workqueue kcopyd: flags=0x8
[67501.195885] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195896] pending: do_work [dm_mod]
[67501.195920] workqueue kcopyd: flags=0x8
[67501.195924] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=2/256
[67501.195935] in-flight: 67:do_work [dm_mod]
[67501.195945] pending: do_work [dm_mod]
[67501.195961] pool 8: cpus=4 node=0 flags=0x0 nice=0 hung=27s workers=3 idle: 129 23765
The root cause for these issues is the way dm-snapshot uses kcopyd. In
particular, the lack of an explicit or implicit limit to the maximum
number of in-flight COW jobs. The merging path is not affected because
it implicitly limits the in-flight kcopyd jobs to one.
Fix these issues by using a semaphore to limit the maximum number of
in-flight kcopyd jobs. We grab the semaphore before allocating a new
kcopyd job in start_copy() and start_full_bio() and release it after the
job finishes in copy_callback().
The initial semaphore value is configurable through a module parameter,
to allow fine tuning the maximum number of in-flight COW jobs. Setting
this parameter to zero initializes the semaphore to INT_MAX.
A default value of 2048 maximum in-flight kcopyd jobs was chosen. This
value was decided experimentally as a trade-off between memory
consumption, stalling the kernel's workqueues and maintaining a high
enough throughput.
Re-running the aforementioned test:
* Workqueue stalls are eliminated
* kcopyd's job slab cache uses a maximum of 130MB
* The time taken by the test to write to the snapshot-origin target is
reduced from 05m20.48s to 03m26.38s
[1] https://github.com/jthornber/device-mapper-test-suite
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-10-31 17:53:08 -04:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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dm snapshot: Fix excessive memory usage and workqueue stalls
kcopyd has no upper limit to the number of jobs one can allocate and
issue. Under certain workloads this can lead to excessive memory usage
and workqueue stalls. For example, when creating multiple dm-snapshot
targets with a 4K chunk size and then writing to the origin through the
page cache. Syncing the page cache causes a large number of BIOs to be
issued to the dm-snapshot origin target, which itself issues an even
larger (because of the BIO splitting taking place) number of kcopyd
jobs.
Running the following test, from the device mapper test suite [1],
dmtest run --suite snapshot -n many_snapshots_of_same_volume_N
, with 8 active snapshots, results in the kcopyd job slab cache growing
to 10G. Depending on the available system RAM this can lead to the OOM
killer killing user processes:
[463.492878] kthreadd invoked oom-killer: gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP),
nodemask=(null), order=1, oom_score_adj=0
[463.492894] kthreadd cpuset=/ mems_allowed=0
[463.492948] CPU: 7 PID: 2 Comm: kthreadd Not tainted 4.19.0-rc7 #3
[463.492950] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[463.492952] Call Trace:
[463.492964] dump_stack+0x7d/0xbb
[463.492973] dump_header+0x6b/0x2fc
[463.492987] ? lockdep_hardirqs_on+0xee/0x190
[463.493012] oom_kill_process+0x302/0x370
[463.493021] out_of_memory+0x113/0x560
[463.493030] __alloc_pages_slowpath+0xf40/0x1020
[463.493055] __alloc_pages_nodemask+0x348/0x3c0
[463.493067] cache_grow_begin+0x81/0x8b0
[463.493072] ? cache_grow_begin+0x874/0x8b0
[463.493078] fallback_alloc+0x1e4/0x280
[463.493092] kmem_cache_alloc_node+0xd6/0x370
[463.493098] ? copy_process.part.31+0x1c5/0x20d0
[463.493105] copy_process.part.31+0x1c5/0x20d0
[463.493115] ? __lock_acquire+0x3cc/0x1550
[463.493121] ? __switch_to_asm+0x34/0x70
[463.493129] ? kthread_create_worker_on_cpu+0x70/0x70
[463.493135] ? finish_task_switch+0x90/0x280
[463.493165] _do_fork+0xe0/0x6d0
[463.493191] ? kthreadd+0x19f/0x220
[463.493233] kernel_thread+0x25/0x30
[463.493235] kthreadd+0x1bf/0x220
[463.493242] ? kthread_create_on_cpu+0x90/0x90
[463.493248] ret_from_fork+0x3a/0x50
[463.493279] Mem-Info:
[463.493285] active_anon:20631 inactive_anon:4831 isolated_anon:0
[463.493285] active_file:80216 inactive_file:80107 isolated_file:435
[463.493285] unevictable:0 dirty:51266 writeback:109372 unstable:0
[463.493285] slab_reclaimable:31191 slab_unreclaimable:3483521
[463.493285] mapped:526 shmem:4903 pagetables:1759 bounce:0
[463.493285] free:33623 free_pcp:2392 free_cma:0
...
[463.493489] Unreclaimable slab info:
[463.493513] Name Used Total
[463.493522] bio-6 1028KB 1028KB
[463.493525] bio-5 1028KB 1028KB
[463.493528] dm_snap_pending_exception 236783KB 243789KB
[463.493531] dm_exception 41KB 42KB
[463.493534] bio-4 1216KB 1216KB
[463.493537] bio-3 439396KB 439396KB
[463.493539] kcopyd_job 6973427KB 6973427KB
...
[463.494340] Out of memory: Kill process 1298 (ruby2.3) score 1 or sacrifice child
[463.494673] Killed process 1298 (ruby2.3) total-vm:435740kB, anon-rss:20180kB, file-rss:4kB, shmem-rss:0kB
[463.506437] oom_reaper: reaped process 1298 (ruby2.3), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
Moreover, issuing a large number of kcopyd jobs results in kcopyd
hogging the CPU, while processing them. As a result, processing of work
items, queued for execution on the same CPU as the currently running
kcopyd thread, is stalled for long periods of time, hurting performance.
Running the aforementioned test we get, in dmesg, messages like the
following:
[67501.194592] BUG: workqueue lockup - pool cpus=4 node=0 flags=0x0 nice=0 stuck for 27s!
[67501.195586] Showing busy workqueues and worker pools:
[67501.195591] workqueue events: flags=0x0
[67501.195597] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195611] pending: cache_reap
[67501.195641] workqueue mm_percpu_wq: flags=0x8
[67501.195645] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195656] pending: vmstat_update
[67501.195682] workqueue kblockd: flags=0x18
[67501.195687] pwq 5: cpus=2 node=0 flags=0x0 nice=-20 active=1/256
[67501.195698] pending: blk_timeout_work
[67501.195753] workqueue kcopyd: flags=0x8
[67501.195757] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195768] pending: do_work [dm_mod]
[67501.195802] workqueue kcopyd: flags=0x8
[67501.195806] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195817] pending: do_work [dm_mod]
[67501.195834] workqueue kcopyd: flags=0x8
[67501.195838] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195848] pending: do_work [dm_mod]
[67501.195881] workqueue kcopyd: flags=0x8
[67501.195885] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195896] pending: do_work [dm_mod]
[67501.195920] workqueue kcopyd: flags=0x8
[67501.195924] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=2/256
[67501.195935] in-flight: 67:do_work [dm_mod]
[67501.195945] pending: do_work [dm_mod]
[67501.195961] pool 8: cpus=4 node=0 flags=0x0 nice=0 hung=27s workers=3 idle: 129 23765
The root cause for these issues is the way dm-snapshot uses kcopyd. In
particular, the lack of an explicit or implicit limit to the maximum
number of in-flight COW jobs. The merging path is not affected because
it implicitly limits the in-flight kcopyd jobs to one.
Fix these issues by using a semaphore to limit the maximum number of
in-flight kcopyd jobs. We grab the semaphore before allocating a new
kcopyd job in start_copy() and start_full_bio() and release it after the
job finishes in copy_callback().
The initial semaphore value is configurable through a module parameter,
to allow fine tuning the maximum number of in-flight COW jobs. Setting
this parameter to zero initializes the semaphore to INT_MAX.
A default value of 2048 maximum in-flight kcopyd jobs was chosen. This
value was decided experimentally as a trade-off between memory
consumption, stalling the kernel's workqueues and maintaining a high
enough throughput.
Re-running the aforementioned test:
* Workqueue stalls are eliminated
* kcopyd's job slab cache uses a maximum of 130MB
* The time taken by the test to write to the snapshot-origin target is
reduced from 05m20.48s to 03m26.38s
[1] https://github.com/jthornber/device-mapper-test-suite
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-10-31 17:53:08 -04:00
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2013-03-01 22:45:49 +00:00
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2010-08-12 04:13:51 +01:00
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2009-12-10 23:52:12 +00:00
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2009-04-02 19:55:34 +01:00
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2007-07-12 17:26:32 +01:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2011-08-02 12:32:04 +01:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
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2018-08-07 16:56:00 -04:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
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2011-08-02 12:32:04 +01:00
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2005-04-16 15:20:36 -07:00
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2006-12-06 20:33:20 -08:00
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2005-04-16 15:20:36 -07:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:41 +00:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:38 +00:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:33 +00:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:33 +00:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:41 +00:00
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2008-07-21 12:00:32 +01:00
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2012-12-21 20:23:41 +00:00
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2008-07-21 12:00:32 +01:00
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2008-07-21 12:00:34 +01:00
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hlist: drop the node parameter from iterators
I'm not sure why, but the hlist for each entry iterators were conceived
list_for_each_entry(pos, head, member)
The hlist ones were greedy and wanted an extra parameter:
hlist_for_each_entry(tpos, pos, head, member)
Why did they need an extra pos parameter? I'm not quite sure. Not only
they don't really need it, it also prevents the iterator from looking
exactly like the list iterator, which is unfortunate.
Besides the semantic patch, there was some manual work required:
- Fix up the actual hlist iterators in linux/list.h
- Fix up the declaration of other iterators based on the hlist ones.
- A very small amount of places were using the 'node' parameter, this
was modified to use 'obj->member' instead.
- Coccinelle didn't handle the hlist_for_each_entry_safe iterator
properly, so those had to be fixed up manually.
The semantic patch which is mostly the work of Peter Senna Tschudin is here:
@@
iterator name hlist_for_each_entry, hlist_for_each_entry_continue, hlist_for_each_entry_from, hlist_for_each_entry_rcu, hlist_for_each_entry_rcu_bh, hlist_for_each_entry_continue_rcu_bh, for_each_busy_worker, ax25_uid_for_each, ax25_for_each, inet_bind_bucket_for_each, sctp_for_each_hentry, sk_for_each, sk_for_each_rcu, sk_for_each_from, sk_for_each_safe, sk_for_each_bound, hlist_for_each_entry_safe, hlist_for_each_entry_continue_rcu, nr_neigh_for_each, nr_neigh_for_each_safe, nr_node_for_each, nr_node_for_each_safe, for_each_gfn_indirect_valid_sp, for_each_gfn_sp, for_each_host;
type T;
expression a,c,d,e;
identifier b;
statement S;
@@
-T b;
<+... when != b
(
hlist_for_each_entry(a,
- b,
c, d) S
|
hlist_for_each_entry_continue(a,
- b,
c) S
|
hlist_for_each_entry_from(a,
- b,
c) S
|
hlist_for_each_entry_rcu(a,
- b,
c, d) S
|
hlist_for_each_entry_rcu_bh(a,
- b,
c, d) S
|
hlist_for_each_entry_continue_rcu_bh(a,
- b,
c) S
|
for_each_busy_worker(a, c,
- b,
d) S
|
ax25_uid_for_each(a,
- b,
c) S
|
ax25_for_each(a,
- b,
c) S
|
inet_bind_bucket_for_each(a,
- b,
c) S
|
sctp_for_each_hentry(a,
- b,
c) S
|
sk_for_each(a,
- b,
c) S
|
sk_for_each_rcu(a,
- b,
c) S
|
sk_for_each_from
-(a, b)
+(a)
S
+ sk_for_each_from(a) S
|
sk_for_each_safe(a,
- b,
c, d) S
|
sk_for_each_bound(a,
- b,
c) S
|
hlist_for_each_entry_safe(a,
- b,
c, d, e) S
|
hlist_for_each_entry_continue_rcu(a,
- b,
c) S
|
nr_neigh_for_each(a,
- b,
c) S
|
nr_neigh_for_each_safe(a,
- b,
c, d) S
|
nr_node_for_each(a,
- b,
c) S
|
nr_node_for_each_safe(a,
- b,
c, d) S
|
- for_each_gfn_sp(a, c, d, b) S
+ for_each_gfn_sp(a, c, d) S
|
- for_each_gfn_indirect_valid_sp(a, c, d, b) S
+ for_each_gfn_indirect_valid_sp(a, c, d) S
|
for_each_host(a,
- b,
c) S
|
for_each_host_safe(a,
- b,
c, d) S
|
for_each_mesh_entry(a,
- b,
c, d) S
)
...+>
[akpm@linux-foundation.org: drop bogus change from net/ipv4/raw.c]
[akpm@linux-foundation.org: drop bogus hunk from net/ipv6/raw.c]
[akpm@linux-foundation.org: checkpatch fixes]
[akpm@linux-foundation.org: fix warnings]
[akpm@linux-foudnation.org: redo intrusive kvm changes]
Tested-by: Peter Senna Tschudin <peter.senna@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-02-27 17:06:00 -08:00
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2008-07-21 12:00:34 +01:00
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2009-12-10 23:52:29 +00:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:34 +00:00
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2005-04-16 15:20:36 -07:00
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treewide: kmalloc() -> kmalloc_array()
The kmalloc() function has a 2-factor argument form, kmalloc_array(). This
patch replaces cases of:
kmalloc(a * b, gfp)
with:
kmalloc_array(a * b, gfp)
as well as handling cases of:
kmalloc(a * b * c, gfp)
with:
kmalloc(array3_size(a, b, c), gfp)
as it's slightly less ugly than:
kmalloc_array(array_size(a, b), c, gfp)
This does, however, attempt to ignore constant size factors like:
kmalloc(4 * 1024, gfp)
though any constants defined via macros get caught up in the conversion.
Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.
The tools/ directory was manually excluded, since it has its own
implementation of kmalloc().
The Coccinelle script used for this was:
// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@
(
kmalloc(
- (sizeof(TYPE)) * E
+ sizeof(TYPE) * E
, ...)
|
kmalloc(
- (sizeof(THING)) * E
+ sizeof(THING) * E
, ...)
)
// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@
(
kmalloc(
- sizeof(u8) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(__u8) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(char) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(unsigned char) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(u8) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(__u8) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(char) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(unsigned char) * COUNT
+ COUNT
, ...)
)
// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@
(
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (COUNT_ID)
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * COUNT_ID
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (COUNT_CONST)
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * COUNT_CONST
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (COUNT_ID)
+ COUNT_ID, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * COUNT_ID
+ COUNT_ID, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (COUNT_CONST)
+ COUNT_CONST, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * COUNT_CONST
+ COUNT_CONST, sizeof(THING)
, ...)
)
// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@
- kmalloc
+ kmalloc_array
(
- SIZE * COUNT
+ COUNT, SIZE
, ...)
// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@
(
kmalloc(
- sizeof(TYPE) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(THING) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
)
// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@
(
kmalloc(
- sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kmalloc(
- sizeof(THING1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(THING1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
)
// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@
(
kmalloc(
- (COUNT) * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
)
// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@
(
kmalloc(C1 * C2 * C3, ...)
|
kmalloc(
- (E1) * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- (E1) * (E2) * E3
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- (E1) * (E2) * (E3)
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- E1 * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
)
// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@
(
kmalloc(sizeof(THING) * C2, ...)
|
kmalloc(sizeof(TYPE) * C2, ...)
|
kmalloc(C1 * C2 * C3, ...)
|
kmalloc(C1 * C2, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (E2)
+ E2, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * E2
+ E2, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (E2)
+ E2, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * E2
+ E2, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- (E1) * E2
+ E1, E2
, ...)
|
- kmalloc
+ kmalloc_array
(
- (E1) * (E2)
+ E1, E2
, ...)
|
- kmalloc
+ kmalloc_array
(
- E1 * E2
+ E1, E2
, ...)
)
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 13:55:00 -07:00
|
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|
2005-04-16 15:20:36 -07:00
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|
|
2015-02-26 11:40:35 -05:00
|
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|
|
2005-04-16 15:20:36 -07:00
|
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|
2015-02-26 11:40:35 -05:00
|
|
|
|
treewide: kmalloc() -> kmalloc_array()
The kmalloc() function has a 2-factor argument form, kmalloc_array(). This
patch replaces cases of:
kmalloc(a * b, gfp)
with:
kmalloc_array(a * b, gfp)
as well as handling cases of:
kmalloc(a * b * c, gfp)
with:
kmalloc(array3_size(a, b, c), gfp)
as it's slightly less ugly than:
kmalloc_array(array_size(a, b), c, gfp)
This does, however, attempt to ignore constant size factors like:
kmalloc(4 * 1024, gfp)
though any constants defined via macros get caught up in the conversion.
Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.
The tools/ directory was manually excluded, since it has its own
implementation of kmalloc().
The Coccinelle script used for this was:
// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@
(
kmalloc(
- (sizeof(TYPE)) * E
+ sizeof(TYPE) * E
, ...)
|
kmalloc(
- (sizeof(THING)) * E
+ sizeof(THING) * E
, ...)
)
// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@
(
kmalloc(
- sizeof(u8) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(__u8) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(char) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(unsigned char) * (COUNT)
+ COUNT
, ...)
|
kmalloc(
- sizeof(u8) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(__u8) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(char) * COUNT
+ COUNT
, ...)
|
kmalloc(
- sizeof(unsigned char) * COUNT
+ COUNT
, ...)
)
// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@
(
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (COUNT_ID)
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * COUNT_ID
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (COUNT_CONST)
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * COUNT_CONST
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (COUNT_ID)
+ COUNT_ID, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * COUNT_ID
+ COUNT_ID, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (COUNT_CONST)
+ COUNT_CONST, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * COUNT_CONST
+ COUNT_CONST, sizeof(THING)
, ...)
)
// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@
- kmalloc
+ kmalloc_array
(
- SIZE * COUNT
+ COUNT, SIZE
, ...)
// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@
(
kmalloc(
- sizeof(TYPE) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(TYPE) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kmalloc(
- sizeof(THING) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kmalloc(
- sizeof(THING) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
)
// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@
(
kmalloc(
- sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kmalloc(
- sizeof(THING1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(THING1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
|
kmalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
)
// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@
(
kmalloc(
- (COUNT) * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- (COUNT) * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kmalloc(
- COUNT * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
)
// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@
(
kmalloc(C1 * C2 * C3, ...)
|
kmalloc(
- (E1) * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- (E1) * (E2) * E3
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- (E1) * (E2) * (E3)
+ array3_size(E1, E2, E3)
, ...)
|
kmalloc(
- E1 * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
)
// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@
(
kmalloc(sizeof(THING) * C2, ...)
|
kmalloc(sizeof(TYPE) * C2, ...)
|
kmalloc(C1 * C2 * C3, ...)
|
kmalloc(C1 * C2, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * (E2)
+ E2, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(TYPE) * E2
+ E2, sizeof(TYPE)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * (E2)
+ E2, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- sizeof(THING) * E2
+ E2, sizeof(THING)
, ...)
|
- kmalloc
+ kmalloc_array
(
- (E1) * E2
+ E1, E2
, ...)
|
- kmalloc
+ kmalloc_array
(
- (E1) * (E2)
+ E1, E2
, ...)
|
- kmalloc
+ kmalloc_array
(
- E1 * E2
+ E1, E2
, ...)
)
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 13:55:00 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2007-07-12 17:26:32 +01:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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|
2009-12-10 23:52:24 +00:00
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|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2008-10-30 13:33:12 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2008-10-30 13:33:12 +00:00
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2005-04-16 15:20:36 -07:00
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2008-10-30 13:33:12 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2014-01-13 19:13:36 -05:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2014-01-13 19:13:36 -05:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2008-07-21 12:00:35 +01:00
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2005-04-16 15:20:36 -07:00
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2018-05-20 18:25:53 -04:00
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2008-07-21 12:00:35 +01:00
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2008-10-30 13:33:16 +00:00
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2008-07-21 12:00:35 +01:00
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2005-04-16 15:20:36 -07:00
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2007-07-12 17:26:32 +01:00
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2005-04-16 15:20:36 -07:00
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2008-10-30 13:33:16 +00:00
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2018-05-20 18:25:53 -04:00
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2014-03-17 18:06:10 +01:00
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2008-10-30 13:33:16 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2008-02-08 02:11:27 +00:00
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2019-03-17 14:22:57 +02:00
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2009-12-10 23:52:10 +00:00
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2008-02-08 02:11:27 +00:00
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2019-03-17 14:22:57 +02:00
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2008-02-08 02:11:27 +00:00
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2009-12-10 23:52:11 +00:00
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2008-02-08 02:11:27 +00:00
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2009-12-10 23:52:11 +00:00
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2008-02-08 02:11:27 +00:00
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2019-03-17 14:22:57 +02:00
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2008-02-08 02:11:27 +00:00
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2019-03-17 14:22:57 +02:00
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2008-02-08 02:11:27 +00:00
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2009-01-06 03:05:19 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2009-01-06 03:05:19 +00:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2014-01-13 19:13:36 -05:00
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2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2019-03-17 14:22:57 +02:00
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2009-12-10 23:52:11 +00:00
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2019-03-17 14:22:57 +02:00
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2008-02-08 02:11:27 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:08 +00:00
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2012-07-27 15:08:00 +01:00
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2009-12-10 23:52:08 +00:00
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2012-07-27 15:08:00 +01:00
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2009-12-10 23:52:08 +00:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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2013-09-18 19:40:42 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:12 +00:00
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2005-04-16 15:20:36 -07:00
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2013-09-18 19:40:42 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:51:54 +00:00
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2008-02-08 02:10:06 +00:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:32 +00:00
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2014-03-17 18:06:10 +01:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
|
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|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:33 +00:00
|
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|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:33 +00:00
|
|
|
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|
2009-12-10 23:52:32 +00:00
|
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|
2009-12-10 23:52:34 +00:00
|
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|
2009-12-10 23:52:32 +00:00
|
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:35 +00:00
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2009-12-10 23:52:32 +00:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:35 +00:00
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|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:35 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:34 +00:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
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|
2009-12-10 23:52:33 +00:00
|
|
|
|
2009-12-10 23:52:34 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:34 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:35 +00:00
|
|
|
|
2009-12-10 23:52:33 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:32 +00:00
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sched: Remove proliferation of wait_on_bit() action functions
The current "wait_on_bit" interface requires an 'action'
function to be provided which does the actual waiting.
There are over 20 such functions, many of them identical.
Most cases can be satisfied by one of just two functions, one
which uses io_schedule() and one which just uses schedule().
So:
Rename wait_on_bit and wait_on_bit_lock to
wait_on_bit_action and wait_on_bit_lock_action
to make it explicit that they need an action function.
Introduce new wait_on_bit{,_lock} and wait_on_bit{,_lock}_io
which are *not* given an action function but implicitly use
a standard one.
The decision to error-out if a signal is pending is now made
based on the 'mode' argument rather than being encoded in the action
function.
All instances of the old wait_on_bit and wait_on_bit_lock which
can use the new version have been changed accordingly and their
action functions have been discarded.
wait_on_bit{_lock} does not return any specific error code in the
event of a signal so the caller must check for non-zero and
interpolate their own error code as appropriate.
The wait_on_bit() call in __fscache_wait_on_invalidate() was
ambiguous as it specified TASK_UNINTERRUPTIBLE but used
fscache_wait_bit_interruptible as an action function.
David Howells confirms this should be uniformly
"uninterruptible"
The main remaining user of wait_on_bit{,_lock}_action is NFS
which needs to use a freezer-aware schedule() call.
A comment in fs/gfs2/glock.c notes that having multiple 'action'
functions is useful as they display differently in the 'wchan'
field of 'ps'. (and /proc/$PID/wchan).
As the new bit_wait{,_io} functions are tagged "__sched", they
will not show up at all, but something higher in the stack. So
the distinction will still be visible, only with different
function names (gds2_glock_wait versus gfs2_glock_dq_wait in the
gfs2/glock.c case).
Since first version of this patch (against 3.15) two new action
functions appeared, on in NFS and one in CIFS. CIFS also now
uses an action function that makes the same freezer aware
schedule call as NFS.
Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: David Howells <dhowells@redhat.com> (fscache, keys)
Acked-by: Steven Whitehouse <swhiteho@redhat.com> (gfs2)
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steve French <sfrench@samba.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140707051603.28027.72349.stgit@notabene.brown
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-07-07 15:16:04 +10:00
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2009-12-10 23:52:32 +00:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2019-06-19 17:05:54 -04:00
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2008-07-21 12:00:32 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:12 +00:00
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2016-02-02 12:29:18 +08:00
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2013-03-01 22:45:47 +00:00
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2009-12-10 23:52:31 +00:00
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2005-04-16 15:20:36 -07:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:12 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:31 +00:00
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2013-03-01 22:45:47 +00:00
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2009-12-10 23:52:31 +00:00
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2018-06-05 05:26:33 -04:00
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2009-12-10 23:52:12 +00:00
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2011-08-02 12:32:03 +01:00
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2009-12-10 23:52:12 +00:00
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2019-06-19 17:05:54 -04:00
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2010-08-12 04:13:51 +01:00
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2016-02-02 12:29:18 +08:00
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2010-08-12 04:13:51 +01:00
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2009-12-10 23:52:12 +00:00
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2016-02-02 12:29:18 +08:00
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2011-03-24 13:52:14 +00:00
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2009-12-10 23:52:12 +00:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:12 +00:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:12 +00:00
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2005-04-16 15:20:36 -07:00
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2015-06-21 16:31:33 -04:00
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2006-02-01 03:04:50 -08:00
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2008-10-30 13:33:16 +00:00
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dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
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2018-08-07 16:56:00 -04:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:24 +00:00
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2006-10-03 01:15:30 -07:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:35 +00:00
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2009-12-10 23:52:33 +00:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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dm snapshot: Fix excessive memory usage and workqueue stalls
kcopyd has no upper limit to the number of jobs one can allocate and
issue. Under certain workloads this can lead to excessive memory usage
and workqueue stalls. For example, when creating multiple dm-snapshot
targets with a 4K chunk size and then writing to the origin through the
page cache. Syncing the page cache causes a large number of BIOs to be
issued to the dm-snapshot origin target, which itself issues an even
larger (because of the BIO splitting taking place) number of kcopyd
jobs.
Running the following test, from the device mapper test suite [1],
dmtest run --suite snapshot -n many_snapshots_of_same_volume_N
, with 8 active snapshots, results in the kcopyd job slab cache growing
to 10G. Depending on the available system RAM this can lead to the OOM
killer killing user processes:
[463.492878] kthreadd invoked oom-killer: gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP),
nodemask=(null), order=1, oom_score_adj=0
[463.492894] kthreadd cpuset=/ mems_allowed=0
[463.492948] CPU: 7 PID: 2 Comm: kthreadd Not tainted 4.19.0-rc7 #3
[463.492950] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[463.492952] Call Trace:
[463.492964] dump_stack+0x7d/0xbb
[463.492973] dump_header+0x6b/0x2fc
[463.492987] ? lockdep_hardirqs_on+0xee/0x190
[463.493012] oom_kill_process+0x302/0x370
[463.493021] out_of_memory+0x113/0x560
[463.493030] __alloc_pages_slowpath+0xf40/0x1020
[463.493055] __alloc_pages_nodemask+0x348/0x3c0
[463.493067] cache_grow_begin+0x81/0x8b0
[463.493072] ? cache_grow_begin+0x874/0x8b0
[463.493078] fallback_alloc+0x1e4/0x280
[463.493092] kmem_cache_alloc_node+0xd6/0x370
[463.493098] ? copy_process.part.31+0x1c5/0x20d0
[463.493105] copy_process.part.31+0x1c5/0x20d0
[463.493115] ? __lock_acquire+0x3cc/0x1550
[463.493121] ? __switch_to_asm+0x34/0x70
[463.493129] ? kthread_create_worker_on_cpu+0x70/0x70
[463.493135] ? finish_task_switch+0x90/0x280
[463.493165] _do_fork+0xe0/0x6d0
[463.493191] ? kthreadd+0x19f/0x220
[463.493233] kernel_thread+0x25/0x30
[463.493235] kthreadd+0x1bf/0x220
[463.493242] ? kthread_create_on_cpu+0x90/0x90
[463.493248] ret_from_fork+0x3a/0x50
[463.493279] Mem-Info:
[463.493285] active_anon:20631 inactive_anon:4831 isolated_anon:0
[463.493285] active_file:80216 inactive_file:80107 isolated_file:435
[463.493285] unevictable:0 dirty:51266 writeback:109372 unstable:0
[463.493285] slab_reclaimable:31191 slab_unreclaimable:3483521
[463.493285] mapped:526 shmem:4903 pagetables:1759 bounce:0
[463.493285] free:33623 free_pcp:2392 free_cma:0
...
[463.493489] Unreclaimable slab info:
[463.493513] Name Used Total
[463.493522] bio-6 1028KB 1028KB
[463.493525] bio-5 1028KB 1028KB
[463.493528] dm_snap_pending_exception 236783KB 243789KB
[463.493531] dm_exception 41KB 42KB
[463.493534] bio-4 1216KB 1216KB
[463.493537] bio-3 439396KB 439396KB
[463.493539] kcopyd_job 6973427KB 6973427KB
...
[463.494340] Out of memory: Kill process 1298 (ruby2.3) score 1 or sacrifice child
[463.494673] Killed process 1298 (ruby2.3) total-vm:435740kB, anon-rss:20180kB, file-rss:4kB, shmem-rss:0kB
[463.506437] oom_reaper: reaped process 1298 (ruby2.3), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
Moreover, issuing a large number of kcopyd jobs results in kcopyd
hogging the CPU, while processing them. As a result, processing of work
items, queued for execution on the same CPU as the currently running
kcopyd thread, is stalled for long periods of time, hurting performance.
Running the aforementioned test we get, in dmesg, messages like the
following:
[67501.194592] BUG: workqueue lockup - pool cpus=4 node=0 flags=0x0 nice=0 stuck for 27s!
[67501.195586] Showing busy workqueues and worker pools:
[67501.195591] workqueue events: flags=0x0
[67501.195597] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195611] pending: cache_reap
[67501.195641] workqueue mm_percpu_wq: flags=0x8
[67501.195645] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195656] pending: vmstat_update
[67501.195682] workqueue kblockd: flags=0x18
[67501.195687] pwq 5: cpus=2 node=0 flags=0x0 nice=-20 active=1/256
[67501.195698] pending: blk_timeout_work
[67501.195753] workqueue kcopyd: flags=0x8
[67501.195757] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195768] pending: do_work [dm_mod]
[67501.195802] workqueue kcopyd: flags=0x8
[67501.195806] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195817] pending: do_work [dm_mod]
[67501.195834] workqueue kcopyd: flags=0x8
[67501.195838] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195848] pending: do_work [dm_mod]
[67501.195881] workqueue kcopyd: flags=0x8
[67501.195885] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=1/256
[67501.195896] pending: do_work [dm_mod]
[67501.195920] workqueue kcopyd: flags=0x8
[67501.195924] pwq 8: cpus=4 node=0 flags=0x0 nice=0 active=2/256
[67501.195935] in-flight: 67:do_work [dm_mod]
[67501.195945] pending: do_work [dm_mod]
[67501.195961] pool 8: cpus=4 node=0 flags=0x0 nice=0 hung=27s workers=3 idle: 129 23765
The root cause for these issues is the way dm-snapshot uses kcopyd. In
particular, the lack of an explicit or implicit limit to the maximum
number of in-flight COW jobs. The merging path is not affected because
it implicitly limits the in-flight kcopyd jobs to one.
Fix these issues by using a semaphore to limit the maximum number of
in-flight kcopyd jobs. We grab the semaphore before allocating a new
kcopyd job in start_copy() and start_full_bio() and release it after the
job finishes in copy_callback().
The initial semaphore value is configurable through a module parameter,
to allow fine tuning the maximum number of in-flight COW jobs. Setting
this parameter to zero initializes the semaphore to INT_MAX.
A default value of 2048 maximum in-flight kcopyd jobs was chosen. This
value was decided experimentally as a trade-off between memory
consumption, stalling the kernel's workqueues and maintaining a high
enough throughput.
Re-running the aforementioned test:
* Workqueue stalls are eliminated
* kcopyd's job slab cache uses a maximum of 130MB
* The time taken by the test to write to the snapshot-origin target is
reduced from 05m20.48s to 03m26.38s
[1] https://github.com/jthornber/device-mapper-test-suite
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-10-31 17:53:08 -04:00
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2013-03-01 22:45:49 +00:00
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2011-05-29 13:03:13 +01:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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2018-05-20 18:25:53 -04:00
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2008-07-21 12:00:35 +01:00
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2009-04-02 19:55:34 +01:00
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2008-07-21 12:00:35 +01:00
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2008-07-21 12:00:32 +01:00
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2009-12-10 23:52:24 +00:00
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2013-03-01 22:45:47 +00:00
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2019-06-19 17:05:54 -04:00
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2016-01-31 13:28:26 -05:00
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2009-12-10 23:52:24 +00:00
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2009-04-02 19:55:31 +01:00
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2007-07-12 17:28:13 +01:00
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2006-10-03 01:15:25 -07:00
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2009-12-10 23:52:24 +00:00
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2007-07-12 17:28:13 +01:00
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2006-10-03 01:15:25 -07:00
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2006-02-01 03:04:50 -08:00
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2009-10-16 23:18:16 +01:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2012-07-27 15:08:00 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2009-04-02 19:55:34 +01:00
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2018-05-20 18:25:53 -04:00
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2009-04-02 19:55:34 +01:00
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2008-04-24 21:43:19 +01:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:11 +00:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:12 +00:00
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2010-08-12 04:13:51 +01:00
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2019-06-19 17:05:54 -04:00
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2009-12-10 23:52:12 +00:00
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2005-04-16 15:20:36 -07:00
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2006-12-08 02:41:11 -08:00
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2008-04-24 21:43:19 +01:00
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2006-12-08 02:41:11 -08:00
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2009-12-10 23:52:11 +00:00
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2006-12-08 02:41:11 -08:00
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2009-12-10 23:52:24 +00:00
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2015-10-08 18:05:41 -04:00
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2009-12-10 23:52:24 +00:00
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2012-07-27 15:08:00 +01:00
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2009-12-10 23:52:24 +00:00
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2015-06-21 16:31:33 -04:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2008-07-21 12:00:32 +01:00
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2007-07-12 17:26:32 +01:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
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2009-12-10 23:52:24 +00:00
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|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2006-03-27 01:17:50 -08:00
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2005-04-16 15:20:36 -07:00
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2008-10-30 13:33:16 +00:00
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2009-01-06 03:04:54 +00:00
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2008-10-30 13:33:16 +00:00
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2018-05-20 18:25:53 -04:00
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2008-10-30 13:33:16 +00:00
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2008-07-21 12:00:32 +01:00
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2006-12-08 02:41:11 -08:00
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2005-04-16 15:20:36 -07:00
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2018-05-20 18:25:53 -04:00
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2008-07-21 12:00:35 +01:00
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2009-04-02 19:55:34 +01:00
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2006-03-27 01:17:50 -08:00
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2009-12-10 23:52:12 +00:00
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2010-08-12 04:13:51 +01:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2005-04-16 15:20:36 -07:00
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|
2019-10-02 06:14:17 -04:00
|
|
|
|
|
|
|
|
|
dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
|
|
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|
|
2019-10-02 06:14:17 -04:00
|
|
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|
|
|
|
|
|
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|
|
|
|
|
|
|
|
|
dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
|
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2019-10-02 06:14:17 -04:00
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2005-04-16 15:20:36 -07:00
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|
dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
|
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|
2009-12-10 23:52:30 +00:00
|
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|
dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
|
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|
2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2007-09-27 12:47:43 +02:00
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2005-04-16 15:20:36 -07:00
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2006-10-03 01:15:31 -07:00
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2006-03-27 01:17:45 -08:00
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2009-04-02 19:55:31 +01:00
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2006-03-27 01:17:45 -08:00
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2009-12-10 23:52:12 +00:00
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2006-03-27 01:17:45 -08:00
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dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2016-01-08 19:07:55 -05:00
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2005-04-16 15:20:36 -07:00
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2016-01-08 19:07:55 -05:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2006-10-03 01:15:29 -07:00
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2011-08-02 12:32:04 +01:00
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2019-03-17 14:22:57 +02:00
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2006-10-03 01:15:29 -07:00
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2005-04-16 15:20:36 -07:00
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2019-03-17 14:22:57 +02:00
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2006-03-27 01:17:45 -08:00
|
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|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2006-10-03 01:15:29 -07:00
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2019-03-17 14:22:57 +02:00
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2006-03-27 01:17:45 -08:00
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2014-01-13 19:13:36 -05:00
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2006-03-27 01:17:45 -08:00
|
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|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
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|
|
|
2006-03-27 01:17:45 -08:00
|
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|
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|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2009-12-10 23:52:11 +00:00
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
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|
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|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2009-12-10 23:52:11 +00:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
2011-08-02 12:32:03 +01:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
2009-12-10 23:52:11 +00:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2009-12-10 23:52:30 +00:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
2015-11-25 16:03:31 -05:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
2009-12-10 23:52:34 +00:00
|
|
|
|
|
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
|
|
|
|
|
2015-07-20 15:29:37 +02:00
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
2006-10-03 01:15:29 -07:00
|
|
|
|
2009-12-10 23:52:30 +00:00
|
|
|
|
2015-02-17 14:34:00 -05:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2016-01-08 19:07:55 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2008-03-28 14:16:10 -07:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2007-07-12 17:26:32 +01:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
|
|
|
|
|
2018-08-07 16:56:00 -04:00
|
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|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2018-08-07 16:56:00 -04:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
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|
2019-10-02 06:14:17 -04:00
|
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|
2005-04-16 15:20:36 -07:00
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|
2007-07-12 17:26:32 +01:00
|
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|
2005-04-16 15:20:36 -07:00
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|
2008-04-24 21:43:17 +01:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:33 +01:00
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2009-10-16 23:18:17 +01:00
|
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2005-04-16 15:20:36 -07:00
|
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2009-12-10 23:52:12 +00:00
|
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|
2009-04-02 19:55:33 +01:00
|
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2005-04-16 15:20:36 -07:00
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|
2019-10-02 06:14:17 -04:00
|
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|
|
2011-08-02 12:32:03 +01:00
|
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|
|
2005-04-16 15:20:36 -07:00
|
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|
|
|
|
|
|
|
2015-07-20 15:29:37 +02:00
|
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|
|
2011-08-02 12:32:04 +01:00
|
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|
|
|
|
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|
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|
2017-06-03 09:38:06 +02:00
|
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|
2011-08-02 12:32:04 +01:00
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2019-10-02 06:14:17 -04:00
|
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|
2011-08-02 12:32:04 +01:00
|
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2009-04-02 19:55:25 +01:00
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|
2009-12-10 23:52:11 +00:00
|
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|
2009-04-02 19:55:25 +01:00
|
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2005-04-16 15:20:36 -07:00
|
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|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2007-07-12 17:26:32 +01:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
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|
2009-04-02 19:55:31 +01:00
|
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|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
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|
2006-03-27 01:17:45 -08:00
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dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
dm snapshot: avoid snapshot space leak on crash
There is a possible leak of snapshot space in case of crash.
The reason for space leaking is that chunks in the snapshot device are
allocated sequentially, but they are finished (and stored in the metadata)
out of order, depending on the order in which copying finished.
For example, supposed that the metadata contains the following records
SUPERBLOCK
METADATA (blocks 0 ... 250)
DATA 0
DATA 1
DATA 2
...
DATA 250
Now suppose that you allocate 10 new data blocks 251-260. Suppose that
copying of these blocks finish out of order (block 260 finished first
and the block 251 finished last). Now, the snapshot device looks like
this:
SUPERBLOCK
METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256)
DATA 0
DATA 1
DATA 2
...
DATA 250
DATA 251
DATA 252
DATA 253
DATA 254
DATA 255
METADATA (blocks 255, 254, 253, 252, 251)
DATA 256
DATA 257
DATA 258
DATA 259
DATA 260
Now, if the machine crashes after writing the first metadata block but
before writing the second metadata block, the space for areas DATA 250-255
is leaked, it contains no valid data and it will never be used in the
future.
This patch makes dm-snapshot complete exceptions in the same order they
were allocated, thus fixing this bug.
Note: when backporting this patch to the stable kernel, change the version
field in the following way:
* if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0}
* if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it
to {1, 10, 2}
Userspace reads the version to determine if the bug was fixed, so the
version change is needed.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2013-11-29 18:13:37 -05:00
|
|
|
|
2009-12-10 23:52:11 +00:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
|
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
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2009-12-10 23:52:10 +00:00
|
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|
|
2008-02-08 02:11:27 +00:00
|
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2005-04-16 15:20:36 -07:00
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2017-08-23 19:10:32 +02:00
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2013-10-11 15:44:27 -07:00
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2005-04-16 15:20:36 -07:00
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2019-06-19 17:05:54 -04:00
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2019-10-02 06:14:17 -04:00
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2019-06-19 17:05:54 -04:00
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2019-10-02 06:14:17 -04:00
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2019-06-19 17:05:54 -04:00
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2012-12-21 20:23:41 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:10 +00:00
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2007-07-12 17:26:32 +01:00
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2006-12-08 02:41:06 -08:00
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2005-04-16 15:20:36 -07:00
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2007-07-12 17:26:32 +01:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2012-12-21 20:23:41 +00:00
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2016-08-05 15:35:16 -06:00
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2017-08-23 19:10:32 +02:00
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2009-06-22 10:12:25 +01:00
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2013-10-11 15:44:27 -07:00
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2019-03-17 14:22:57 +02:00
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2005-04-16 15:20:36 -07:00
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2006-03-27 01:17:45 -08:00
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2005-04-16 15:20:36 -07:00
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2017-06-03 09:38:02 +02:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2019-03-17 14:22:57 +02:00
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2006-10-03 01:15:28 -07:00
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2016-07-19 11:28:41 +02:00
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2017-06-03 09:38:02 +02:00
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2006-10-03 01:15:28 -07:00
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2019-06-19 17:05:54 -04:00
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2006-10-03 01:15:28 -07:00
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2009-12-10 23:52:11 +00:00
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2006-10-03 01:15:28 -07:00
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2008-02-08 02:11:27 +00:00
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2019-06-19 17:05:54 -04:00
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2006-10-03 01:15:28 -07:00
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2005-04-16 15:20:36 -07:00
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2016-07-19 11:28:41 +02:00
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2009-04-02 19:55:25 +01:00
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2006-03-27 01:17:45 -08:00
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2019-03-17 14:22:57 +02:00
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2009-04-02 19:55:25 +01:00
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2019-03-17 14:22:57 +02:00
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2009-04-02 19:55:25 +01:00
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2009-12-10 23:52:11 +00:00
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2009-04-02 19:55:26 +01:00
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2009-04-02 19:55:25 +01:00
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2009-04-02 19:55:25 +01:00
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2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
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|
|
|
|
|
|
|
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2015-10-08 18:05:41 -04:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2015-10-08 18:05:41 -04:00
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2019-03-17 14:22:57 +02:00
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2017-06-03 09:38:02 +02:00
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|
2019-03-17 14:22:57 +02:00
|
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|
2009-04-02 19:55:25 +01:00
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|
2005-04-16 15:20:36 -07:00
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2008-02-08 02:11:27 +00:00
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2006-03-27 01:17:45 -08:00
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|
2006-12-08 02:41:06 -08:00
|
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|
|
2006-10-03 01:15:28 -07:00
|
|
|
|
2019-06-19 17:05:54 -04:00
|
|
|
|
2011-08-02 12:32:04 +01:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
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|
2011-08-02 12:32:04 +01:00
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|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
|
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
2006-10-03 01:15:28 -07:00
|
|
|
|
|
|
|
|
|
2008-07-21 12:00:32 +01:00
|
|
|
|
2017-08-23 19:10:32 +02:00
|
|
|
|
2012-12-21 20:23:41 +00:00
|
|
|
|
2008-07-21 12:00:32 +01:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2011-08-02 12:32:03 +01:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2011-08-02 12:32:03 +01:00
|
|
|
|
2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:31 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:31 +00:00
|
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|
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2012-12-21 20:23:41 +00:00
|
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2009-12-10 23:52:31 +00:00
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2012-12-21 20:23:41 +00:00
|
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|
|
|
|
|
|
2016-08-05 15:35:16 -06:00
|
|
|
|
2013-03-01 22:45:47 +00:00
|
|
|
|
2017-08-23 19:10:32 +02:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
|
|
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2017-08-23 19:10:32 +02:00
|
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|
2009-12-10 23:52:31 +00:00
|
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2019-07-17 11:12:30 -04:00
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2013-10-11 15:44:27 -07:00
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2009-12-10 23:52:31 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
|
|
|
2009-12-10 23:52:36 +00:00
|
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2009-12-10 23:52:31 +00:00
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|
|
2009-12-10 23:52:33 +00:00
|
|
|
|
2016-07-19 11:28:41 +02:00
|
|
|
|
2009-12-10 23:52:33 +00:00
|
|
|
|
|
|
|
|
|
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|
|
2017-08-23 19:10:32 +02:00
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|
2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:33 +00:00
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2009-12-10 23:52:31 +00:00
|
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|
|
2009-12-10 23:52:33 +00:00
|
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|
|
2016-07-19 11:28:41 +02:00
|
|
|
|
2012-12-21 20:23:41 +00:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
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2009-12-10 23:52:36 +00:00
|
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|
|
2017-08-23 19:10:32 +02:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
|
|
|
2016-07-19 11:28:41 +02:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:31 +00:00
|
|
|
|
|
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|
|
2017-06-03 09:38:06 +02:00
|
|
|
|
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|
|
2008-07-21 12:00:32 +01:00
|
|
|
|
|
|
|
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|
|
2012-12-21 20:23:41 +00:00
|
|
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|
|
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|
2008-07-21 12:00:32 +01:00
|
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|
2017-06-03 09:38:03 +02:00
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2008-07-21 12:00:32 +01:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:24 +00:00
|
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|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
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|
2009-12-10 23:52:24 +00:00
|
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|
2011-01-13 19:59:59 +00:00
|
|
|
|
2009-12-10 23:52:24 +00:00
|
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|
|
|
|
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|
|
|
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|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
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2005-04-16 15:20:36 -07:00
|
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|
|
2007-07-12 17:26:32 +01:00
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
|
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
|
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
|
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
2009-12-10 23:52:32 +00:00
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
|
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
|
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
2015-02-26 11:40:35 -05:00
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
|
|
|
|
|
dm snapshot: suspend merging snapshot when doing exception handover
The "dm snapshot: suspend origin when doing exception handover" commit
fixed a exception store handover bug associated with pending exceptions
to the "snapshot-origin" target.
However, a similar problem exists in snapshot merging. When snapshot
merging is in progress, we use the target "snapshot-merge" instead of
"snapshot-origin". Consequently, during exception store handover, we
must find the snapshot-merge target and suspend its associated
mapped_device.
To avoid lockdep warnings, the target must be suspended and resumed
without holding _origins_lock.
Introduce a dm_hold() function that grabs a reference on a
mapped_device, but unlike dm_get(), it doesn't crash if the device has
the DMF_FREEING flag set, it returns an error in this case.
In snapshot_resume() we grab the reference to the origin device using
dm_hold() while holding _origins_lock (_origins_lock guarantees that the
device won't disappear). Then we release _origins_lock, suspend the
device and grab _origins_lock again.
NOTE to stable@ people:
When backporting to kernels 3.18 and older, use dm_internal_suspend and
dm_internal_resume instead of dm_internal_suspend_fast and
dm_internal_resume_fast.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2015-02-26 11:41:28 -05:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2009-12-10 23:52:24 +00:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2006-02-01 03:04:50 -08:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
2012-07-27 15:08:00 +01:00
|
|
|
|
2009-12-10 23:52:32 +00:00
|
|
|
|
2012-07-27 15:08:00 +01:00
|
|
|
|
2009-12-10 23:52:32 +00:00
|
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|
2012-07-27 15:08:00 +01:00
|
|
|
|
2009-12-10 23:52:32 +00:00
|
|
|
|
2012-07-27 15:08:00 +01:00
|
|
|
|
2009-12-10 23:52:32 +00:00
|
|
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|
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|
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|
|
|
|
|
|
2013-03-01 22:45:44 +00:00
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2009-04-02 19:55:34 +01:00
|
|
|
|
2007-07-12 17:26:32 +01:00
|
|
|
|
2019-06-19 17:05:54 -04:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2009-12-10 23:51:53 +00:00
|
|
|
|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:51:53 +00:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2009-12-10 23:52:35 +00:00
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2015-06-21 16:31:33 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:11 +00:00
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2005-04-16 15:20:36 -07:00
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2009-04-02 19:55:34 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:51:53 +00:00
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|
dm snapshot: Replace mutex with rw semaphore
dm-snapshot uses a single mutex to serialize every access to the
snapshot state. This includes all accesses to the complete and pending
exception tables, which occur at every origin write, every snapshot
read/write and every exception completion.
The lock statistics indicate that this mutex is a bottleneck (average
wait time ~480 usecs for 8 processes doing random 4K writes to the
origin device) preventing dm-snapshot to scale as the number of threads
doing IO increases.
The major contention points are __origin_write()/snapshot_map() and
pending_complete(), i.e., the submission and completion of pending
exceptions.
Replace this mutex with a rw semaphore.
We essentially revert commit ae1093be5a0ef9 ("dm snapshot: use mutex
instead of rw_semaphore") and together with the next two patches we
substitute the single mutex with a fine-grained locking scheme, where we
use a read-write semaphore to protect the mostly read fields of the
snapshot structure, e.g., valid, active, etc., and per-bucket bit
spinlocks to protect accesses to the complete and pending exception
tables.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:56 +02:00
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2009-12-10 23:51:53 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:12 +00:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2009-09-04 20:40:19 +01:00
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2010-08-12 04:13:50 +01:00
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2009-09-04 20:40:19 +01:00
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2010-08-12 04:13:50 +01:00
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2009-09-04 20:40:19 +01:00
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2019-06-19 17:05:54 -04:00
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2019-07-17 11:12:30 -04:00
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2019-06-19 17:05:54 -04:00
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2019-07-17 11:12:30 -04:00
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2019-06-19 17:05:54 -04:00
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2009-09-04 20:40:19 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:28 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
|
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2009-12-10 23:52:10 +00:00
|
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|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
2009-12-10 23:52:30 +00:00
|
|
|
|
|
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
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2009-12-10 23:52:31 +00:00
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2005-07-12 15:53:05 -07:00
|
|
|
|
2009-12-10 23:52:28 +00:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
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|
|
|
|
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|
2009-12-10 23:52:28 +00:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
|
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2005-04-16 15:20:36 -07:00
|
|
|
|
2009-04-02 19:55:25 +01:00
|
|
|
|
2006-03-27 01:17:45 -08:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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|
|
|
|
|
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|
|
|
|
|
|
|
|
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2009-04-02 19:55:25 +01:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
2009-04-02 19:55:25 +01:00
|
|
|
|
dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
|
|
|
|
2019-03-17 14:22:57 +02:00
|
|
|
|
dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2019-03-17 14:22:57 +02:00
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dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
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2009-04-02 19:55:26 +01:00
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dm snapshot: Don't sleep holding the snapshot lock
When completing a pending exception, pending_complete() waits for all
conflicting reads to drain, before inserting the final, completed
exception. Conflicting reads are snapshot reads redirected to the
origin, because the relevant chunk is not remapped to the COW device the
moment we receive the read.
The completed exception must be inserted into the exception table after
all conflicting reads drain to ensure snapshot reads don't return
corrupted data. This is required because inserting the completed
exception into the exception table signals that the relevant chunk is
remapped and both origin writes and snapshot merging will now overwrite
the chunk in origin.
This wait is done holding the snapshot lock to ensure that
pending_complete() doesn't starve if new snapshot reads keep coming for
this chunk.
In preparation for the next commit, where we use a spinlock instead of a
mutex to protect the exception tables, we remove the need for holding
the lock while waiting for conflicting reads to drain.
We achieve this in two steps:
1. pending_complete() inserts the completed exception before waiting for
conflicting reads to drain and removes the pending exception after
all conflicting reads drain.
This ensures that new snapshot reads will be redirected to the COW
device, instead of the origin, and thus pending_complete() will not
starve. Moreover, we use the existence of both a completed and
a pending exception to signify that the COW is done but there are
conflicting reads in flight.
2. In __origin_write() we check first if there is a pending exception
and then if there is a completed exception. If there is a pending
exception any submitted BIO is delayed on the pe->origin_bios list and
DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the
origin nor snapshot merging can overwrite the origin chunk, until all
conflicting reads drain, and thus snapshot reads will not return
corrupted data.
Summarizing, we now have the following possible combinations of pending
and completed exceptions for a chunk, along with their meaning:
A. No exceptions exist: The chunk has not been remapped yet.
B. Only a pending exception exists: The chunk is currently being copied
to the COW device.
C. Both a pending and a completed exception exist: COW for this chunk
has completed but there are snapshot reads in flight which had been
redirected to the origin before the chunk was remapped.
D. Only the completed exception exists: COW has been completed and there
are no conflicting reads in flight.
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:55 +02:00
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2009-04-02 19:55:25 +01:00
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2006-03-27 01:17:45 -08:00
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2009-12-10 23:52:30 +00:00
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2006-03-27 01:17:45 -08:00
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2009-12-10 23:52:30 +00:00
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2006-03-27 01:17:45 -08:00
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2009-12-10 23:52:30 +00:00
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2006-03-27 01:17:45 -08:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2011-08-02 12:32:03 +01:00
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2019-03-17 14:22:57 +02:00
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dm snapshot: Use fine-grained locking scheme
Substitute the global locking scheme with a fine grained one, employing
the read-write semaphore and the scalable exception tables with
per-bucket locks introduced by the previous two commits.
Summarizing, we now use a read-write semaphore to protect the mostly
read fields of the snapshot structure, e.g., valid, active, etc., and
per-bucket bit spinlocks to protect accesses to the complete and pending
exception tables.
Finally, we use an extra spinlock (pe_allocation_lock) to serialize the
allocation of new exceptions by the exception store. This allocation is
really fast, so the extra spinlock doesn't hurt the performance.
This scheme allows dm-snapshot to scale better, resulting in increased
IOPS and reduced latency.
Following are some benchmark results using the null_blk device:
modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \
queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1
* Benchmark fio_origin_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to origin device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 57708 | 66421 |
| 2 | 63415 | 77589 |
| 4 | 67276 | 98839 |
| 8 | 60564 | 109258 |
+--------------+-------------+------------+
* Benchmark fio_origin_randwrite_latency_N, from the device mapper test
suite [1] (direct IO, random 4K writes to origin device, IO engine
psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 16.25 | 13.27 |
| 2 | 31.65 | 25.08 |
| 4 | 55.28 | 41.08 |
| 8 | 121.47 | 74.44 |
+--------------+-----------------------+----------------------+
* Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine libaio):
+--------------+-------------+------------+
| # of workers | IOPS Before | IOPS After |
+--------------+-------------+------------+
| 1 | 72593 | 84938 |
| 2 | 97379 | 134973 |
| 4 | 90610 | 143077 |
| 8 | 90537 | 180085 |
+--------------+-------------+------------+
* Benchmark fio_snapshot_randwrite_latency_N, from the device mapper
test suite [1] (direct IO, random 4K writes to snapshot device, IO
engine psync):
+--------------+-----------------------+----------------------+
| # of workers | Latency (usec) Before | Latency (usec) After |
+--------------+-----------------------+----------------------+
| 1 | 12.53 | 10.6 |
| 2 | 19.78 | 14.89 |
| 4 | 40.37 | 23.47 |
| 8 | 89.32 | 48.48 |
+--------------+-----------------------+----------------------+
[1] https://github.com/jthornber/device-mapper-test-suite
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-03-17 14:22:58 +02:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2006-03-27 01:17:44 -08:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2005-04-16 15:20:36 -07:00
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2006-12-08 02:41:06 -08:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2013-10-11 15:44:27 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:34 +00:00
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2012-07-27 15:08:00 +01:00
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2009-12-10 23:52:34 +00:00
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2012-07-27 15:08:00 +01:00
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2009-12-10 23:52:34 +00:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2006-06-26 00:27:35 -07:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2014-03-14 18:42:12 -04:00
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2013-03-01 22:45:47 +00:00
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2009-06-22 10:12:25 +01:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2015-02-26 11:40:35 -05:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2012-12-21 20:23:41 +00:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2014-03-14 18:43:07 -04:00
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2005-04-16 15:20:36 -07:00
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2017-08-23 19:10:32 +02:00
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2005-04-16 15:20:36 -07:00
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2016-08-05 15:35:16 -06:00
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2009-06-22 10:12:25 +01:00
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2016-07-19 11:28:41 +02:00
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2009-06-22 10:12:25 +01:00
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2014-03-14 18:43:07 -04:00
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2005-04-16 15:20:36 -07:00
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dm snapshot: rework COW throttling to fix deadlock
Commit 721b1d98fb517a ("dm snapshot: Fix excessive memory usage and
workqueue stalls") introduced a semaphore to limit the maximum number of
in-flight kcopyd (COW) jobs.
The implementation of this throttling mechanism is prone to a deadlock:
1. One or more threads write to the origin device causing COW, which is
performed by kcopyd.
2. At some point some of these threads might reach the s->cow_count
semaphore limit and block in down(&s->cow_count), holding a read lock
on _origins_lock.
3. Someone tries to acquire a write lock on _origins_lock, e.g.,
snapshot_ctr(), which blocks because the threads at step (2) already
hold a read lock on it.
4. A COW operation completes and kcopyd runs dm-snapshot's completion
callback, which ends up calling pending_complete().
pending_complete() tries to resubmit any deferred origin bios. This
requires acquiring a read lock on _origins_lock, which blocks.
This happens because the read-write semaphore implementation gives
priority to writers, meaning that as soon as a writer tries to enter
the critical section, no readers will be allowed in, until all
writers have completed their work.
So, pending_complete() waits for the writer at step (3) to acquire
and release the lock. This writer waits for the readers at step (2)
to release the read lock and those readers wait for
pending_complete() (the kcopyd thread) to signal the s->cow_count
semaphore: DEADLOCK.
The above was thoroughly analyzed and documented by Nikos Tsironis as
part of his initial proposal for fixing this deadlock, see:
https://www.redhat.com/archives/dm-devel/2019-October/msg00001.html
Fix this deadlock by reworking COW throttling so that it waits without
holding any locks. Add a variable 'in_progress' that counts how many
kcopyd jobs are running. A function wait_for_in_progress() will sleep if
'in_progress' is over the limit. It drops _origins_lock in order to
avoid the deadlock.
Reported-by: Guruswamy Basavaiah <guru2018@gmail.com>
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Reviewed-by: Nikos Tsironis <ntsironis@arrikto.com>
Tested-by: Nikos Tsironis <ntsironis@arrikto.com>
Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
Cc: stable@vger.kernel.org # v5.0+
Depends-on: 4a3f111a73a8c ("dm snapshot: introduce account_start_copy() and account_end_copy()")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-10-02 06:15:53 -04:00
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2005-04-16 15:20:36 -07:00
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2012-07-27 15:08:00 +01:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:43:07 -04:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2013-03-01 22:45:44 +00:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2014-03-14 18:42:12 -04:00
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2005-04-16 15:20:36 -07:00
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2009-09-04 20:40:19 +01:00
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2014-03-14 18:42:12 -04:00
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2009-09-04 20:40:19 +01:00
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2014-03-14 18:42:12 -04:00
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2009-09-04 20:40:19 +01:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2015-02-26 11:40:35 -05:00
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2005-04-16 15:20:36 -07:00
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2009-09-04 20:40:19 +01:00
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2005-04-16 15:20:36 -07:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2008-07-21 12:00:32 +01:00
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2009-12-10 23:52:24 +00:00
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2005-04-16 15:20:36 -07:00
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2009-09-04 20:40:19 +01:00
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2019-06-19 17:05:54 -04:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2019-06-19 17:05:54 -04:00
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2009-12-10 23:52:30 +00:00
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2009-12-10 23:52:31 +00:00
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2009-12-10 23:52:30 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:30 +00:00
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2009-12-10 23:52:32 +00:00
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2009-12-10 23:52:30 +00:00
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2019-06-19 17:05:54 -04:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-01-06 03:05:17 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:10 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2007-07-12 17:26:32 +01:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2017-11-25 01:43:50 +08:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-10-16 23:18:14 +01:00
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2017-11-25 01:43:50 +08:00
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2009-10-16 23:18:14 +01:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-01-06 03:04:58 +00:00
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2009-12-10 23:52:30 +00:00
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2005-04-16 15:20:36 -07:00
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2009-01-06 03:05:17 +00:00
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2005-04-16 15:20:36 -07:00
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2013-03-01 22:45:47 +00:00
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