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Shakeel Butt fefc6e6631 memcg: rearrange fields of mem_cgroup_per_node 
Kernel test robot reported [1] performance regression for will-it-scale
test suite's page_fault2 test case for the commit 70a64b7919 ("memcg:
dynamically allocate lruvec_stats").  After inspection it seems like the
commit has unintentionally introduced false cache sharing.

After the commit the fields of mem_cgroup_per_node which get read on the
performance critical path share the cacheline with the fields which get
updated often on LRU page allocations or deallocations.  This has caused
contention on that cacheline and the workloads which manipulates a lot of
LRU pages are regressed as reported by the test report.

The solution is to rearrange the fields of mem_cgroup_per_node such that
the false sharing is eliminated.  Let's move all the read only pointers at
the start of the struct, followed by memcg-v1 only fields and at the end
fields which get updated often.

Experiment setup: Ran fallocate1, fallocate2, page_fault1, page_fault2 and
page_fault3 from the will-it-scale test suite inside a three level memcg
with /tmp mounted as tmpfs on two different machines, one a single numa
node and the other one, two node machine.

 $ ./[testcase]_processes -t $NR_CPUS -s 50

Results for single node, 52 CPU machine:

Testcase        base        with-patch

fallocate1      1031081     1431291  (38.80 %)
fallocate2      1029993     1421421  (38.00 %)
page_fault1     2269440     3405788  (50.07 %)
page_fault2     2375799     3572868  (50.30 %)
page_fault3     28641143    28673950 ( 0.11 %)

Results for dual node, 80 CPU machine:

Testcase        base        with-patch

fallocate1      2976288     3641185  (22.33 %)
fallocate2      2979366     3638181  (22.11 %)
page_fault1     6221790     7748245  (24.53 %)
page_fault2     6482854     7847698  (21.05 %)
page_fault3     28804324    28991870 ( 0.65 %)

Link: https://lkml.kernel.org/r/20240528164050.2625718-1-shakeel.butt@linux.dev
Fixes: 70a64b7919 ("memcg: dynamically allocate lruvec_stats")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reported-by: kernel test robot <oliver.sang@intel.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Feng Tang <feng.tang@intel.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-07-03 19:30:02 -07:00
arch mm: remove page_mapping() 2024-07-03 19:29:59 -07:00
block block: unmap and free user mapped integrity via submitter 2024-06-12 11:00:50 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation mm/vmscan: update stale references to shrink_page_list 2024-07-03 19:29:52 -07:00
drivers ata fixes for 6.10-rc6 2024-06-30 14:32:24 -07:00
fs mm: remove MIGRATE_SYNC_NO_COPY mode 2024-07-03 19:30:00 -07:00
include memcg: rearrange fields of mem_cgroup_per_node 2024-07-03 19:30:02 -07:00
init gcc: disable '-Warray-bounds' for gcc-9 2024-06-15 10:43:04 -07:00
io_uring io_uring: signal SQPOLL task_work with TWA_SIGNAL_NO_IPI 2024-06-24 19:46:15 -06:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel mm: remove the implementation of swap_free() and always use swap_free_nr() 2024-07-03 19:30:01 -07:00
lib hardening fixes for v6.10-rc6 2024-06-28 16:11:02 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/hugetlb: mm/memory_hotplug: use a folio in scan_movable_pages() 2024-07-03 19:30:02 -07:00
net NFS client bugfixes for Linux 6.10 2024-06-29 13:48:24 -07:00
rust rust: avoid unused import warning in rusttest 2024-06-11 23:33:28 +02:00
samples tracing/treewide: Remove second parameter of __assign_str() 2024-05-22 20:14:47 -04:00
scripts kbuild: scripts/gdb: bring the "abspath" back 2024-06-27 04:20:32 +09:00
security lsm/stable-6.10 PR 20240617 2024-06-17 18:35:12 -07:00
sound ASoC: Fixes for v6.10 2024-06-26 22:02:55 +02:00
tools selftest: mm: Test if hugepage does not get leaked during __bio_release_pages() 2024-07-03 19:29:59 -07:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt KVM fixes for 6.10 2024-06-21 08:03:55 -04:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap bpf-for-netdev 2024-06-14 17:57:10 -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 MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
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 IOMMU Fixes for Linux v6.10-rc5 2024-06-28 09:18:01 -07:00
Makefile Linux 6.10-rc6 2024-06-30 14:40:44 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.