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Shakeel Butt 11192d9c12 memcg: flush stats only if updated 
At the moment, the kernel flushes the memcg stats on every refault and
also on every reclaim iteration.  Although rstat maintains per-cpu
update tree but on the flush the kernel still has to go through all the
cpu rstat update tree to check if there is anything to flush.  This
patch adds the tracking on the stats update side to make flush side more
clever by skipping the flush if there is no update.

The stats update codepath is very sensitive performance wise for many
workloads and benchmarks.  So, we can not follow what the commit
aa48e47e39 ("memcg: infrastructure to flush memcg stats") did which
was triggering async flush through queue_work() and caused a lot
performance regression reports.  That got reverted by the commit
1f828223b7 ("memcg: flush lruvec stats in the refault").

In this patch we kept the stats update codepath very minimal and let the
stats reader side to flush the stats only when the updates are over a
specific threshold.  For now the threshold is (nr_cpus * CHARGE_BATCH).

To evaluate the impact of this patch, an 8 GiB tmpfs file is created on
a system with swap-on-zram and the file was pushed to swap through
memory.force_empty interface.  On reading the whole file, the memcg stat
flush in the refault code path is triggered.  With this patch, we
observed 63% reduction in the read time of 8 GiB file.

Link: https://lkml.kernel.org/r/20211001190040.48086-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Reviewed-by: "Michal Koutný" <mkoutny@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
History 2021-11-06 13:30:35 -07:00
arch * Fixes for s390 interrupt delivery 2021-10-31 11:19:02 -07:00
block block-5.15-2021-10-29 2021-10-29 11:10:29 -07:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-08-30 12:57:10 -07:00
Documentation Networking fixes for 5.15-rc8/final, including fixes from WiFi 2021-10-28 10:17:31 -07:00
drivers mtd: call bdi_unregister explicitly 2021-11-06 13:30:34 -07:00
fs fs: explicitly unregister per-superblock BDIs 2021-11-06 13:30:34 -07:00
include mm: simplify bdi refcounting 2021-11-06 13:30:34 -07:00
init mm: disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT 2021-11-06 13:30:33 -07:00
ipc ipc: remove memcg accounting for sops objects in do_semtimedop() 2021-09-14 10:22:11 -07:00
kernel workqueue, kasan: avoid alloc_pages() when recording stack 2021-11-06 13:30:33 -07:00
lib kasan: test: bypass __alloc_size checks 2021-11-06 13:30:33 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm memcg: flush stats only if updated 2021-11-06 13:30:35 -07:00
net mptcp: fix corrupt receiver key in MPC + data + checksum 2021-10-28 08:19:06 -07:00
samples samples/bpf: Relicense bpf_insn.h as GPL-2.0-only OR BSD-2-Clause 2021-09-29 16:03:55 +02:00
scripts Compiler Attributes: add __alloc_size() for better bounds checking 2021-11-06 13:30:33 -07:00
security Merge branch 'ucount-fixes-for-v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2021-10-21 17:27:17 -10:00
sound ALSA: usb-audio: Fix microphone sound on Jieli webcam. 2021-10-19 08:07:01 +02:00
tools perf script: Fix PERF_SAMPLE_WEIGHT_STRUCT support 2021-10-31 12:51:41 -03:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Remove tlbs_dirty 2021-09-23 11:01:12 -04:00
.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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.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 drm fixes for 5.15 final 2021-10-28 12:17:01 -07:00
Makefile Compiler Attributes: add __alloc_size() for better bounds checking 2021-11-06 13:30:33 -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.