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Chuck Lever d06b86a75b svcrdma: Increase the per-transport rw_ctx count 
[ Upstream commit 2da0f610e7 ]

rdma_rw_mr_factor() returns the smallest number of MRs needed to
move a particular number of pages. svcrdma currently asks for the
number of MRs needed to move RPCSVC_MAXPAGES (a little over one
megabyte), as that is the number of pages in the largest r/wsize
the server supports.

This call assumes that the client's NIC can bundle a full one
megabyte payload in a single rdma_segment. In fact, most NICs cannot
handle a full megabyte with a single rkey / rdma_segment. Clients
will typically split even a single Read chunk into many segments.

The server needs one MR to read each rdma_segment in a Read chunk,
and thus each one needs an rw_ctx.

svcrdma has been vastly underestimating the number of rw_ctxs needed
to handle 64 RPC requests with large Read chunks using small
rdma_segments.

Unfortunately there doesn't seem to be a good way to estimate this
number without knowing the client NIC's capabilities. Even then,
the client RPC/RDMA implementation is still free to split a chunk
into smaller segments (for example, it might be using physical
registration, which needs an rdma_segment per page).

The best we can do for now is choose a number that will guarantee
forward progress in the worst case (one page per segment).

At some later point, we could add some mechanisms to make this
much less of a problem:
- Add a core API to add more rw_ctxs to an already-established QP
- svcrdma could treat rw_ctx exhaustion as a temporary error and
  try again
- Limit the number of Reads in flight

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: afcae7d7b8 ("RDMA/core: add rdma_rw_max_sge() helper for SQ sizing")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:19:43 -05:00
arch arm64: dts: qcom: sdm845-db845c: specify power for WiFi CH1 2026-03-04 07:19:30 -05:00
block block,bfq: fix aux stat accumulation destination 2026-02-11 13:35:29 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-02-06 16:41:53 +01:00
Documentation PCI: endpoint: Automatically create a function specific attributes group 2026-02-19 16:21:46 +01:00
drivers RDMA/core: Fix a couple of obvious typos in comments 2026-03-04 07:19:42 -05:00
fs procfs: fix missing RCU protection when reading real_parent in do_task_stat() 2026-03-04 07:19:37 -05:00
include RDMA/core: Fix a couple of obvious typos in comments 2026-03-04 07:19:42 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: fix filename leak in __io_openat_prep() 2026-01-19 13:09:54 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel timers: Replace in_irq() with in_hardirq() 2026-03-04 07:19:36 -05:00
lib lib/crypto: aes: Fix missing MMU protection for AES S-box 2026-01-19 13:10:13 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/kfence: randomize the freelist on initialization 2026-02-11 13:35:27 +01:00
net svcrdma: Increase the per-transport rw_ctx count 2026-03-04 07:19:43 -05:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts kbuild: Use CRC32 and a 1MiB dictionary for XZ compressed modules 2026-01-19 13:10:05 +01:00
security smack: /smack/doi: accept previously used values 2026-03-04 07:19:31 -05:00
sound ASoC: fsl_xcvr: fix missing lock in fsl_xcvr_mode_put() 2026-02-19 16:21:44 +01:00
tools spi: tools: Add include folder to .gitignore 2026-03-04 07:19:32 -05:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:35:27 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.201 2026-02-19 16:21:47 +01:00
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.