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Johannes Weiner 3f1509c57b Revert "mm/vmscan: never demote for memcg reclaim" 
This reverts commit 3a235693d3.

Its premise was that cgroup reclaim cares about freeing memory inside the
cgroup, and demotion just moves them around within the cgroup limit. 
Hence, pages from toptier nodes should be reclaimed directly.

However, with NUMA balancing now doing tier promotions, demotion is part
of the page aging process.  Global reclaim demotes the coldest toptier
pages to secondary memory, where their life continues and from which they
have a chance to get promoted back.  Essentially, tiered memory systems
have an LRU order that spans multiple nodes.

When cgroup reclaims pages coming off the toptier directly, there can be
colder pages on lower tier nodes that were demoted by global reclaim. 
This is an aging inversion, not unlike if cgroups were to reclaim directly
from the active lists while there are inactive pages.

Proactive reclaim is another factor.  The goal of that it is to offload
colder pages from expensive RAM to cheaper storage.  When lower tier
memory is available as an intermediate layer, we want offloading to take
advantage of it instead of bypassing to storage.

Revert the patch so that cgroups respect the LRU order spanning the memory
hierarchy.

Of note is a specific undercommit scenario, where all cgroup limits in the
system add up to <= available toptier memory.  In that case, shuffling
pages out to lower tiers first to reclaim them from there is inefficient. 
This is something could be optimized/short-circuited later on (although
care must be taken not to accidentally recreate the aging inversion). 
Let's ensure correctness first.

Link: https://lkml.kernel.org/r/20220518190911.82400-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-25 10:47:48 -07:00
arch arm64/mm: fix page table check compile error for CONFIG_PGTABLE_LEVELS=2 2022-05-19 14:08:48 -07:00
block block: don't print I/O error warning for dead disks 2022-04-15 06:33:03 -06:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation zswap: memcg accounting 2022-05-19 14:08:53 -07:00
drivers zram: fix Kconfig dependency warning 2022-05-25 10:47:47 -07:00
fs mm: zswap: add basic meminfo and vmstat coverage 2022-05-19 14:08:53 -07:00
include include/trace/events/percpu.h: cleanup for "percpu: improve percpu_alloc_percpu event trace" 2022-05-25 10:47:48 -07:00
init mm: Kconfig: move swap and slab config options to the MM section 2022-05-19 14:08:53 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel mm: khugepaged: make khugepaged_enter() void function 2022-05-19 14:08:49 -07:00
lib mm: fix missing handler for __GFP_NOWARN 2022-05-19 14:08:55 -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 Revert "mm/vmscan: never demote for memcg reclaim" 2022-05-25 10:47:48 -07:00
net tcp: fix F-RTO may not work correctly when receiving DSACK 2022-04-28 10:35:38 -07:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts hardening fixes for v5.18-rc3 2022-04-12 14:29:40 -10:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound ALSA: hda/realtek: Add quirk for Clevo NP70PNP 2022-04-21 21:23:47 +02:00
tools cgroup: fix an error handling path in alloc_pagecache_max_30M() 2022-05-25 10:47:46 -07:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: SEV: add cache flush to solve SEV cache incoherency issues 2022-04-21 15:41:00 -04:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Vasily Averin's email address 2022-04-08 14:20:36 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
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 MAINTAINERS: add Muchun as co-maintainer for HugeTLB 2022-05-25 10:47:47 -07:00
Makefile Linux 5.18-rc4 2022-04-24 14:51:22 -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.