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Kemeng Shi a4d508e333 blk-throttle: simpfy low limit reached check in throtl_tg_can_upgrade 
Commit c79892c557 ("blk-throttle: add upgrade logic for LIMIT_LOW
state") added upgrade logic for low limit and methioned that
1. "To determine if a cgroup exceeds its limitation, we check if the cgroup
has pending request. Since cgroup is throttled according to the limit,
pending request means the cgroup reaches the limit."
2. "If a cgroup has limit set for both read and write, we consider the
combination of them for upgrade. The reason is read IO and write IO can
interfere with each other. If we do the upgrade based in one direction IO,
the other direction IO could be severly harmed."
Besides, we also determine that cgroup reaches low limit if low limit is 0,
see comment in throtl_tg_can_upgrade.

Collect the information above, the desgin of upgrade check is as following:
1.The low limit is reached if limit is zero or io is already queued.
2.Cgroup will pass upgrade check if low limits of READ and WRITE are both
reached.

Simpfy the check code described above to removce repeat check and improve
readability. There is no functional change.

Detail equivalence proof is as following:
All replaced conditions to return true are as following:
condition 1
  (!read_limit && !write_limit)
condition 2
  read_limit && sq->nr_queued[READ] &&
  (!write_limit || sq->nr_queued[WRITE])
condition 3
  write_limit && sq->nr_queued[WRITE] &&
  (!read_limit || sq->nr_queued[READ])

Transferring condition 2 as following:
  (read_limit && sq->nr_queued[READ]) &&
  (!write_limit || sq->nr_queued[WRITE])
is equivalent to
  (read_limit && sq->nr_queued[READ]) &&
  (!write_limit || (write_limit && sq->nr_queued[WRITE]))
is equivalent to
condition 2.1
  (read_limit && sq->nr_queued[READ] &&
  !write_limit) ||
condition 2.2
  (read_limit && sq->nr_queued[READ] &&
  (write_limit && sq->nr_queued[WRITE]))

Transferring condition 3 as following:
  write_limit && sq->nr_queued[WRITE] &&
  (!read_limit || sq->nr_queued[READ])
is equivalent to
  (write_limit && sq->nr_queued[WRITE]) &&
  (!read_limit || (read_limit && sq->nr_queued[READ]))
is equivalent to
condition 3.1
  ((write_limit && sq->nr_queued[WRITE]) &&
  !read_limit) ||
condition 3.2
  ((write_limit && sq->nr_queued[WRITE]) &&
  (read_limit && sq->nr_queued[READ]))

Condition 3.2 is the same as condition 2.2, so all conditions we get to
return are as following:
  (!read_limit && !write_limit) (1)
  (!read_limit && (write_limit && sq->nr_queued[WRITE])) (3.1)
  ((read_limit && sq->nr_queued[READ]) && !write_limit) (2.1)
  ((write_limit && sq->nr_queued[WRITE]) &&
  (read_limit && sq->nr_queued[READ])) (2.2)

As we can extract conditions "(a1 || a2) && (b1 || b2)" to:
a1 && b1
a1 && b2
a2 && b1
ab && b2

Considering that:
a1 = !read_limit
a2 = read_limit && sq->nr_queued[READ]
b1 = !write_limit
b2 = write_limit && sq->nr_queued[WRITE]

We can pack replaced conditions to
  (!read_limit || (read_limit && sq->nr_queued[READ])) &&
  (!write_limit || (write_limit && sq->nr_queued[WRITE]))
which is equivalent to
  (!read_limit || sq->nr_queued[READ]) &&
  (!write_limit || sq->nr_queued[WRITE])

Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Link: https://lore.kernel.org/r/20221205115709.251489-6-shikemeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
History 2022-12-05 13:44:48 -07:00
arch RISC-V: 2022-10-23 15:00:43 -07:00
block blk-throttle: simpfy low limit reached check in throtl_tg_can_upgrade 2022-12-05 13:44:48 -07:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto treewide: use get_random_bytes() when possible 2022-10-11 17:42:58 -06:00
Documentation pktcdvd: remove driver. 2022-12-02 12:35:30 -07:00
drivers floppy: Fix memory leak in do_floppy_init() 2022-12-04 18:03:41 +04:00
fs blk-crypto: add a blk_crypto_config_supported_natively helper 2022-11-21 11:39:05 -07:00
include block: remove devnode callback from struct block_device_operations 2022-12-03 09:19:48 -07:00
init init: Kconfig: fix spelling mistake "satify" -> "satisfy" 2022-10-20 21:27:22 -07:00
io_uring io_uring/rw: enable bio caches for IRQ rw 2022-11-16 09:44:27 -07:00
ipc - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
kernel block: bdev & blktrace: use consistent function doc. notation 2022-12-01 09:16:46 -07:00
lib lru_cache: remove unused lc_private, lc_set, lc_index_of 2022-11-22 19:38:39 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages 2022-11-09 11:29:20 -07:00
net io_uring-6.1-2022-10-22 2022-10-23 09:55:50 -07:00
rust Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
samples VFIO updates for v6.1-rc1 2022-10-12 14:46:48 -07:00
scripts Kbuild fixes for v6.1 2022-10-16 11:12:22 -07:00
security selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context() 2022-10-19 09:55:53 -04:00
sound sound fixes for 6.1-rc1 2022-10-14 13:22:14 -07:00
tools RISC-V: 2022-10-23 15:00:43 -07:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt kvm: Add support for arch compat vm ioctls 2022-10-22 05:15:23 -04:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap mailmap: update email for Qais Yousef 2022-10-20 21:27:21 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS pktcdvd: remove driver. 2022-12-02 12:35:30 -07:00
Makefile Linux 6.1-rc2 2022-10-23 15:27:33 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.