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Muchun Song cae3af62b3 mm: memcontrol: fix swap undercounting in cgroup2
When pages are swapped in, the VM may retain the swap copy to avoid
repeated writes in the future.  It's also retained if shared pages are
faulted back in some processes, but not in others.  During that time we
have an in-memory copy of the page, as well as an on-swap copy.  Cgroup1
and cgroup2 handle these overlapping lifetimes slightly differently due to
the nature of how they account memory and swap:

Cgroup1 has a unified memory+swap counter that tracks a data page
regardless whether it's in-core or swapped out.  On swapin, we transfer
the charge from the swap entry to the newly allocated swapcache page, even
though the swap entry might stick around for a while.  That's why we have
a mem_cgroup_uncharge_swap() call inside mem_cgroup_charge().

Cgroup2 tracks memory and swap as separate, independent resources and thus
has split memory and swap counters.  On swapin, we charge the newly
allocated swapcache page as memory, while the swap slot in turn must
remain charged to the swap counter as long as its allocated too.

The cgroup2 logic was broken by commit 2d1c498072 ("mm: memcontrol: make
swap tracking an integral part of memory control"), because it
accidentally removed the do_memsw_account() check in the branch inside
mem_cgroup_uncharge() that was supposed to tell the difference between the
charge transfer in cgroup1 and the separate counters in cgroup2.

As a result, cgroup2 currently undercounts retained swap to varying
degrees: swap slots are cached up to 50% of the configured limit or total
available swap space; partially faulted back shared pages are only limited
by physical capacity.  This in turn allows cgroups to significantly
overconsume their alloted swap space.

Add the do_memsw_account() check back to fix this problem.

Link: https://lkml.kernel.org/r/20210217153237.92484-1-songmuchun@bytedance.com
Fixes: 2d1c498072 ("mm: memcontrol: make swap tracking an integral part of memory control")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: <stable@vger.kernel.org>	[5.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-02-24 13:38:30 -08:00
arch hexagon: remove CONFIG_EXPERIMENTAL from defconfigs 2021-02-24 13:38:26 -08:00
block for-5.12/block-ipi-2021-02-21 2021-02-22 10:53:05 -08:00
certs certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID 2021-01-21 16:16:10 +00:00
crypto Keyrings miscellany 2021-02-23 16:09:23 -08:00
Documentation mm: memcg: add swapcache stat for memcg v2 2021-02-24 13:38:29 -08:00
drivers mm: memcg: add swapcache stat for memcg v2 2021-02-24 13:38:29 -08:00
fs fs: buffer: use raw page_memcg() on locked page 2021-02-24 13:38:30 -08:00
include fs: buffer: use raw page_memcg() on locked page 2021-02-24 13:38:30 -08:00
init mm, slub: remove slub_memcg_sysfs boot param and CONFIG_SLUB_MEMCG_SYSFS_ON 2021-02-24 13:38:27 -08:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel Keyrings miscellany 2021-02-23 16:09:23 -08:00
lib Modules updates for v5.12 2021-02-23 10:15:33 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm: memcontrol: fix swap undercounting in cgroup2 2021-02-24 13:38:30 -08:00
net idmapped-mounts-v5.12 2021-02-23 13:39:45 -08:00
samples Keyrings miscellany 2021-02-23 16:09:23 -08:00
scripts scripts/spelling.txt: add more spellings to spelling.txt 2021-02-24 13:38:26 -08:00
security Keyrings miscellany 2021-02-23 16:09:23 -08:00
sound ARM updates for 5.12-rc1: 2021-02-22 14:27:07 -08:00
tools clang-lto for v5.12-rc1 (part2) 2021-02-23 15:13:45 -08:00
usr arch: ia64: Remove rest of perfmon support 2021-01-22 12:12:20 +05:30
virt KVM/arm64 fixes for 5.11, take #2 2021-02-12 14:07:39 +00:00
.clang-format clang-format: Update with the latest for_each macro list 2021-01-29 15:00:23 +01:00
.cocciconfig
.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 clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-02-21 17:23:56 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: dccp: move Gerrit Renker to CREDITS 2021-01-14 10:53:49 -08:00
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 dmaengine updates for v5.12-rc1 2021-02-23 15:05:10 -08:00
Makefile clang-lto for v5.12-rc1 (part2) 2021-02-23 15:13:45 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.