drop_slab_node() is called as part of echo 2>/proc/sys/vm/drop_caches
operation.  It iterates over all memcgs and calls shrink_slab() which in
turn iterates over all slab shrinkers.  Freed objects are counted and as
long as the total number of freed objects from all memcgs and shrinkers is
higher than 10, drop_slab_node() loops for another full memcgs*shrinkers
iteration.

This arbitrary constant threshold of 10 can result in effectively an
infinite loop on a system with large number of memcgs and/or parallel
activity that allocates new objects.  This has been reported previously by
Chunxin Zang [1] and recently by our customer.

The previous report [1] has resulted in commit 069c411d ("mm/vmscan:
fix infinite loop in drop_slab_node") which added a check for signals
allowing the user to terminate the command writing to drop_caches.  At the
time it was also considered to make the threshold grow with each iteration
to guarantee termination, but such patch hasn't been formally proposed
yet.

This patch implements the dynamically growing threshold.  At first
iteration it's enough to free one object to continue, and this threshold
effectively doubles with each iteration.  Our customer's feedback was
positive.

There is always a risk that this change will result on some system in a
previously terminating drop_caches operation to terminate sooner and free
fewer objects.  Ideally the semantics would guarantee freeing all freeable
objects that existed at the moment of starting the operation, while not
looping forever for newly allocated objects, but that's not feasible to
track.  In the less ideal solution based on thresholds, arguably the
termination guarantee is more important than the exhaustiveness guarantee.
If there are reports of large regression wrt being exhaustive, we can
tune how fast the threshold grows.

[1] https://lore.kernel.org/lkml/20200909152047.27905-1-zangchunxin@bytedance.com/T/#u

[vbabka@suse.cz: avoid undefined shift behaviour]
  Link: https://lkml.kernel.org/r/2f034e6f-a753-550a-f374-e4e23899d3d5@suse.cz

Link: https://lkml.kernel.org/r/20210818152239.25502-1-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Reported-by: NChunxin Zang <zangchunxin@bytedance.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We could add 'else' to remove the somewhat odd check_pending label to make
code core succinct.

Link: https://lkml.kernel.org/r/20210717065911.61497-5-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shaohua Li <shli@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The return value of kswapd_run() is unused now.  Clean it up.

Link: https://lkml.kernel.org/r/20210717065911.61497-4-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shaohua Li <shli@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The priority field of sc is used to control how many pages we should scan
at once while we always traverse the list to shrink the pages in these
functions.  So these settings are unneeded and misleading.

Link: https://lkml.kernel.org/r/20210717065911.61497-3-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shaohua Li <shli@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Cleanups for vmscan", v2.

This series contains cleanups to remove unneeded return value, misleading
setting and so on.  Also this remove the PageDirty check after MADV_FREE
pages are page_ref_freezed.  More details can be found in the respective
changelogs.

This patch (of 4):

If the MADV_FREE pages are redirtied before they could be reclaimed, put
the pages back to anonymous LRU list by setting SwapBacked flag and the
pages will be reclaimed in normal swapout way.  But as Yu Zhao pointed
out, "The page has only one reference left, which is from the isolation.
After the caller puts the page back on lru and drops the reference, the
page will be freed anyway.  It doesn't matter which lru it goes." So we
don't bother checking PageDirty here.

[Yu Zhao's comment is also quoted in the code.]

Link: https://lkml.kernel.org/r/20210717065911.61497-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210717065911.61497-2-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NYu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Some method is obviously needed to enable reclaim-based migration.

Just like traditional autonuma, there will be some workloads that will
benefit like workloads with more "static" configurations where hot pages
stay hot and cold pages stay cold.  If pages come and go from the hot and
cold sets, the benefits of this approach will be more limited.

The benefits are truly workload-based and *not* hardware-based.  We do not
believe that there is a viable threshold where certain hardware
configurations should have this mechanism enabled while others do not.

To be conservative, earlier work defaulted to disable reclaim- based
migration and did not include a mechanism to enable it.  This proposes add
a new sysfs file

  /sys/kernel/mm/numa/demotion_enabled

as a method to enable it.

We are open to any alternative that allows end users to enable this
mechanism or disable it if workload harm is detected (just like
traditional autonuma).

Once this is enabled page demotion may move data to a NUMA node that does
not fall into the cpuset of the allocating process.  This could be
construed to violate the guarantees of cpusets.  However, since this is an
opt-in mechanism, the assumption is that anyone enabling it is content to
relax the guarantees.

Link: https://lkml.kernel.org/r/20210721063926.3024591-9-ying.huang@intel.com
Link: https://lkml.kernel.org/r/20210715055145.195411-10-ying.huang@intel.comSigned-off-by: NHuang Ying <ying.huang@intel.com>
Originally-by: NDave Hansen <dave.hansen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Global reclaim aims to reduce the amount of memory used on a given node or
set of nodes.  Migrating pages to another node serves this purpose.

memcg reclaim is different.  Its goal is to reduce the total memory
consumption of the entire memcg, across all nodes.  Migration does not
assist memcg reclaim because it just moves page contents between nodes
rather than actually reducing memory consumption.

Link: https://lkml.kernel.org/r/20210715055145.195411-9-ying.huang@intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Suggested-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Reclaim anonymous pages if a migration path is available now that demotion
provides a non-swap recourse for reclaiming anon pages.

Note that this check is subtly different from the can_age_anon_pages()
checks.  This mechanism checks whether a specific page in a specific
context can actually be reclaimed, given current swap space and cgroup
limits.

can_age_anon_pages() is a much simpler and more preliminary check which
just says whether there is a possibility of future reclaim.

[kbusch@kernel.org: v11]
  Link: https://lkml.kernel.org/r/20210715055145.195411-8-ying.huang@intel.com
  Link: https://lkml.kernel.org/r/20210721063926.3024591-7-ying.huang@intel.com

Link: https://lkml.kernel.org/r/20210715055145.195411-8-ying.huang@intel.com
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Anonymous pages are kept on their own LRU(s).  These lists could
theoretically always be scanned and maintained.  But, without swap, there
is currently nothing the kernel can *do* with the results of a scanned,
sorted LRU for anonymous pages.

A check for '!total_swap_pages' currently serves as a valid check as to
whether anonymous LRUs should be maintained.  However, another method will
be added shortly: page demotion.

Abstract out the 'total_swap_pages' checks into a helper, give it a
logically significant name, and check for the possibility of page
demotion.

[dave.hansen@linux.intel.com: v11]
  Link: https://lkml.kernel.org/r/20210715055145.195411-7-ying.huang@intel.com
  Link: https://lkml.kernel.org/r/20210721063926.3024591-6-ying.huang@intel.com

Link: https://lkml.kernel.org/r/20210715055145.195411-7-ying.huang@intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Reviewed-by: NGreg Thelen <gthelen@google.com>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Account the number of demoted pages.

Add pgdemote_kswapd and pgdemote_direct VM counters showed in
/proc/vmstat.

[ daveh:
   - __count_vm_events() a bit, and made them look at the THP
     size directly rather than getting data from migrate_pages()
]

Link: https://lkml.kernel.org/r/20210721063926.3024591-5-ying.huang@intel.com
Link: https://lkml.kernel.org/r/20210715055145.195411-6-ying.huang@intel.comSigned-off-by: NYang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Reviewed-by: NWei Xu <weixugc@google.com>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Greg Thelen <gthelen@google.com>
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This is mostly derived from a patch from Yang Shi:

	https://lore.kernel.org/linux-mm/1560468577-101178-10-git-send-email-yang.shi@linux.alibaba.com/

Add code to the reclaim path (shrink_page_list()) to "demote" data to
another NUMA node instead of discarding the data.  This always avoids the
cost of I/O needed to read the page back in and sometimes avoids the
writeout cost when the page is dirty.

A second pass through shrink_page_list() will be made if any demotions
fail.  This essentially falls back to normal reclaim behavior in the case
that demotions fail.  Previous versions of this patch may have simply
failed to reclaim pages which were eligible for demotion but were unable
to be demoted in practice.

For some cases, for example, MADV_PAGEOUT, the pages are always discarded
instead of demoted to follow the kernel API definition.  Because
MADV_PAGEOUT is defined as freeing specified pages regardless in which
tier they are.

Note: This just adds the start of infrastructure for migration.  It is
actually disabled next to the FIXME in migrate_demote_page_ok().

[dave.hansen@linux.intel.com: v11]
  Link: https://lkml.kernel.org/r/20210715055145.195411-5-ying.huang@intel.com
  Link: https://lkml.kernel.org/r/20210721063926.3024591-4-ying.huang@intel.com

Link: https://lkml.kernel.org/r/20210715055145.195411-5-ying.huang@intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Reviewed-by: NWei Xu <weixugc@google.com>
Reviewed-by: NOscar Salvador <osalvador@suse.de>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

At the moment memcg stats are read in four contexts:

1. memcg stat user interfaces
2. dirty throttling
3. page fault
4. memory reclaim

Currently the kernel flushes the stats for first two cases.  Flushing the
stats for remaining two casese may have performance impact.  Always
flushing the memcg stats on the page fault code path may negatively
impacts the performance of the applications.  In addition flushing in the
memory reclaim code path, though treated as slowpath, can become the
source of contention for the global lock taken for stat flushing because
when system or memcg is under memory pressure, many tasks may enter the
reclaim path.

This patch uses following mechanisms to solve these challenges:

1. Periodically flush the stats from root memcg every 2 seconds.  This
   will time limit the out of sync stats.

2. Asynchronously flush the stats after fixed number of stat updates.
   In the worst case the stat can be out of sync by O(nr_cpus * BATCH) for
   2 seconds.

3. For avoiding thundering herd to flush the stats particularly from
   the memory reclaim context, introduce memcg local spinlock and let only
   one flusher active at a time.  This could have been done through
   cgroup_rstat_lock lock but that lock is used by other subsystem and for
   userspace reading memcg stats.  So, it is better to keep flushers
   introduced by this patch decoupled from cgroup_rstat_lock.  However we
   would have to use irqsafe version of rstat flush but that is fine as
   this code path will be flushing for whole tree and do the work for
   everyone.  No one will be waiting for that worker.

[shakeelb@google.com: fix sleep-in-wrong context bug]
  Link: https://lkml.kernel.org/r/20210716212137.1391164-2-shakeelb@google.com

Link: https://lkml.kernel.org/r/20210714013948.270662-2-shakeelb@google.comSigned-off-by: NShakeel Butt <shakeelb@google.com>
Tested-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The page cache deletion paths all have interrupts enabled, so no need to
use irqsafe/irqrestore locking variants.

They used to have irqs disabled by the memcg lock added in commit
c4843a75 ("memcg: add per cgroup dirty page accounting"), but that has
since been replaced by memcg taking the page lock instead, commit
0a31bc97 ("mm: memcontrol: rewrite uncharge AP").

Link: https://lkml.kernel.org/r/20210614211904.14420-1-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A recent lockdep report included these lines:

[   96.177910] 3 locks held by containerd/770:
[   96.177934]  #0: ffff88810815ea28 (&mm->mmap_lock#2){++++}-{3:3},
at: do_user_addr_fault+0x115/0x770
[   96.177999]  #1: ffffffff82915020 (rcu_read_lock){....}-{1:2}, at:
get_swap_device+0x33/0x140
[   96.178057]  #2: ffffffff82955ba0 (fs_reclaim){+.+.}-{0:0}, at:
__fs_reclaim_acquire+0x5/0x30

While it was not useful to that bug report to know where the reclaim lock
had been acquired, it might be useful under other circumstances.  Allow
the caller of __fs_reclaim_acquire to specify the instruction pointer to
use.

Link: https://lkml.kernel.org/r/20210719185709.1755149-1-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In a debugging session the other day, Rik noticed that node_reclaim()
was missing memstall annotations.  This means we'll miss pressure and
lost productivity resulting from reclaim on an overloaded local NUMA
node when vm.zone_reclaim_mode is enabled.

There haven't been any reports, but that's likely because
vm.zone_reclaim_mode hasn't been a commonly used feature recently, and
the intersection between such setups and psi users is probably nil.

But secondary memory such as CXL-connected DIMMS, persistent memory etc,
and the page demotion patches that handle them
(https://lore.kernel.org/lkml/20210401183216.443C4443@viggo.jf.intel.com/)
could soon make this a more common codepath again.

Link: https://lkml.kernel.org/r/20210818152457.35846-1-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NRik van Riel <riel@surriel.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We've noticed occasional OOM killing when memory.low settings are in
effect for cgroups.  This is unexpected and undesirable as memory.low is
supposed to express non-OOMing memory priorities between cgroups.

The reason for this is proportional memory.low reclaim.  When cgroups
are below their memory.low threshold, reclaim passes them over in the
first round, and then retries if it couldn't find pages anywhere else.
But when cgroups are slightly above their memory.low setting, page scan
force is scaled down and diminished in proportion to the overage, to the
point where it can cause reclaim to fail as well - only in that case we
currently don't retry, and instead trigger OOM.

To fix this, hook proportional reclaim into the same retry logic we have
in place for when cgroups are skipped entirely.  This way if reclaim
fails and some cgroups were scanned with diminished pressure, we'll try
another full-force cycle before giving up and OOMing.

[akpm@linux-foundation.org: coding-style fixes]

Link: https://lkml.kernel.org/r/20210817180506.220056-1-hannes@cmpxchg.org
Fixes: 9783aa99 ("mm, memcg: proportional memory.{low,min} reclaim")
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NLeon Yang <lnyng@fb.com>
Reviewed-by: NRik van Riel <riel@surriel.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NChris Down <chris@chrisdown.name>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>		[5.4+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Clean W=1 build warnings for mm/".

This is a janitorial only.  During development of a tool to catch build
warnings early to avoid tripping the Intel lkp-robot, I noticed that mm/
is not clean for W=1.  This is generally harmless but there is no harm in
cleaning it up.  It disrupts git blame a little but on relatively obvious
lines that are unlikely to be git blame targets.

This patch (of 13):

make W=1 generates the following warning for vmscan.c

    mm/vmscan.c:1814: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

It is not a kerneldoc comment and isolate_lru_pages() is a static
function.  While the detailed comment is nice, it does not need to be
exposed via kernel-doc.

Link: https://lkml.kernel.org/r/20210520084809.8576-1-mgorman@techsingularity.net
Link: https://lkml.kernel.org/r/20210520084809.8576-2-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently try_to_unmap() return bool value by checking page_mapcount(),
however this may return false positive since page_mapcount() doesn't check
all subpages of compound page.  The total_mapcount() could be used
instead, but its cost is higher since it traverses all subpages.

Actually the most callers of try_to_unmap() don't care about the return
value at all.  So just need check if page is still mapped by page_mapped()
when necessary.  And page_mapped() does bail out early when it finds
mapped subpage.

Link: https://lkml.kernel.org/r/bb27e3fe-6036-b637-5086-272befbfe3da@google.comSuggested-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NMinchan Kim <minchan@kernel.org>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: NHugh Dickins <hughd@google.com>
Acked-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Theoretically without the protect from memalloc_noreclaim_save() and
memalloc_noreclaim_restore(), reclaim_pages() can go into the block
I/O layer recursively and deadlock.

Querying 'reclaim_pages' in our kernel crash databases didn't yield
any results. So the deadlock seems unlikely to happen. A possible
explanation is that the only user of reclaim_pages(), i.e.,
MADV_PAGEOUT, is usually called before memory pressure builds up,
e.g., on Android and Chrome OS. Under such a condition, allocations in
the block I/O layer can be fulfilled without diverting to direct
reclaim and therefore the recursion is avoided.

Link: https://lkml.kernel.org/r/20210622074642.785473-1-yuzhao@google.com
Link: https://lkml.kernel.org/r/20210614194727.2684053-1-yuzhao@google.comSigned-off-by: NYu Zhao <yuzhao@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

When kswapd is active then direct reclaim is potentially active.  In
either case, it is possible that a zone would be balanced if pages were
not trapped on PCP lists.  Instead of draining remote pages, simply limit
the size of the PCP lists while kswapd is active.

Link: https://lkml.kernel.org/r/20210525080119.5455-6-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The noinline_for_stack is introduced by commit 66635629 ("vmscan: set
up pagevec as late as possible in shrink_inactive_list()"), its purpose is
to delay the allocation of pagevec as late as possible to save stack
memory.  But the commit 2bcf8879 ("mm: take pagevecs off reclaim
stack") replace pagevecs by lists of pages_to_free.  So we do not need
noinline_for_stack, just remove it (let the compiler decide whether to
inline).

Link: https://lkml.kernel.org/r/20210417043538.9793-9-songmuchun@bytedance.comSigned-off-by: NMuchun Song <songmuchun@bytedance.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lruvec_holds_page_lru_lock() doesn't check anything about locking and is
used to check whether the page belongs to the lruvec.  So rename it to
page_matches_lruvec().

Link: https://lkml.kernel.org/r/20210417043538.9793-6-songmuchun@bytedance.comSigned-off-by: NMuchun Song <songmuchun@bytedance.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Various coding style tweaks to various files under mm/

[daizhiyuan@phytium.com.cn: mm/swapfile: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614223624-16055-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/sparse: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614227288-19363-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/vmscan: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614227649-19853-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/compaction: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614228218-20770-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/oom_kill: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614228360-21168-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/shmem: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614228504-21491-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/page_alloc: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614228613-21754-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/filemap: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1614228936-22337-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/mlock: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1613956588-2453-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/frontswap: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1613962668-15045-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/vmalloc: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1613963379-15988-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/memory_hotplug: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1613971784-24878-1-git-send-email-daizhiyuan@phytium.com.cn
[daizhiyuan@phytium.com.cn: mm/mempolicy: minor coding style tweaks]
  Link: https://lkml.kernel.org/r/1613972228-25501-1-git-send-email-daizhiyuan@phytium.com.cn

Link: https://lkml.kernel.org/r/1614222374-13805-1-git-send-email-daizhiyuan@phytium.com.cnSigned-off-by: NZhiyuan Dai <daizhiyuan@phytium.com.cn>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The number of deferred objects might get windup to an absurd number, and
it results in clamp of slab objects.  It is undesirable for sustaining
workingset.

So shrink deferred objects proportional to priority and cap nr_deferred
to twice of cache items.

The idea is borrowed from Dave Chinner's patch:
  https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.com/

Tested with kernel build and vfs metadata heavy workload in our
production environment, no regression is spotted so far.

Link: https://lkml.kernel.org/r/20210311190845.9708-14-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add
to parent's corresponding nr_deferred when memcg offline.

Link: https://lkml.kernel.org/r/20210311190845.9708-13-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Now nr_deferred is available on per memcg level for memcg aware
shrinkers, so don't need allocate shrinker->nr_deferred for such
shrinkers anymore.

The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or
memcg is disabled by kernel command line, then shrinker's
SHRINKER_MEMCG_AWARE flag would be cleared.  This makes the
implementation of this patch simpler.

Link: https://lkml.kernel.org/r/20210311190845.9708-12-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use per memcg's nr_deferred for memcg aware shrinkers.  The shrinker's
nr_deferred will be used in the following cases:

    1. Non memcg aware shrinkers
    2. !CONFIG_MEMCG
    3. memcg is disabled by boot parameter

Link: https://lkml.kernel.org/r/20210311190845.9708-11-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently the number of deferred objects are per shrinker, but some
slabs, for example, vfs inode/dentry cache are per memcg, this would
result in poor isolation among memcgs.

The deferred objects typically are generated by __GFP_NOFS allocations,
one memcg with excessive __GFP_NOFS allocations may blow up deferred
objects, then other innocent memcgs may suffer from over shrink,
excessive reclaim latency, etc.

For example, two workloads run in memcgA and memcgB respectively,
workload in B is vfs heavy workload.  Workload in A generates excessive
deferred objects, then B's vfs cache might be hit heavily (drop half of
caches) by B's limit reclaim or global reclaim.

We observed this hit in our production environment which was running vfs
heavy workload shown as the below tracing log:

  <...>-409454 [016] .... 28286961.747146: mm_shrink_slab_start: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
  nid: 1 objects to shrink 3641681686040 gfp_flags GFP_HIGHUSER_MOVABLE|__GFP_ZERO pgs_scanned 1 lru_pgs 15721
  cache items 246404277 delta 31345 total_scan 123202138
  <...>-409454 [022] .... 28287105.928018: mm_shrink_slab_end: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
  nid: 1 unused scan count 3641681686040 new scan count 3641798379189 total_scan 602
  last shrinker return val 123186855

The vfs cache and page cache ratio was 10:1 on this machine, and half of
caches were dropped.  This also resulted in significant amount of page
caches were dropped due to inodes eviction.

Make nr_deferred per memcg for memcg aware shrinkers would solve the
unfairness and bring better isolation.

The following patch will add nr_deferred to parent memcg when memcg
offline.  To preserve nr_deferred when reparenting memcgs to root, root
memcg needs shrinker_info allocated too.

When memcg is not enabled (!CONFIG_MEMCG or memcg disabled), the
shrinker's nr_deferred would be used.  And non memcg aware shrinkers use
shrinker's nr_deferred all the time.

Link: https://lkml.kernel.org/r/20210311190845.9708-10-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently registered shrinker is indicated by non-NULL
shrinker->nr_deferred.  This approach is fine with nr_deferred at the
shrinker level, but the following patches will move MEMCG_AWARE
shrinkers' nr_deferred to memcg level, so their shrinker->nr_deferred
would always be NULL.  This would prevent the shrinkers from
unregistering correctly.

Remove SHRINKER_REGISTERING since we could check if shrinker is
registered successfully by the new flag.

Link: https://lkml.kernel.org/r/20210311190845.9708-9-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The shrinker_info is dereferenced in a couple of places via
rcu_dereference_protected with different calling conventions, for
example, using mem_cgroup_nodeinfo helper or dereferencing
memcg->nodeinfo[nid]->shrinker_info.  And the later patch will add more
dereference places.

So extract the dereference into a helper to make the code more readable.
No functional change.

[akpm@linux-foundation.org: retain rcu_dereference_protected() in free_shrinker_info(), per Hugh]

Link: https://lkml.kernel.org/r/20210311190845.9708-8-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The following patch is going to add nr_deferred into shrinker_map, the
change will make shrinker_map not only include map anymore, so rename it
to "memcg_shrinker_info".  And this should make the patch adding
nr_deferred cleaner and readable and make review easier.  Also remove the
"memcg_" prefix.

Link: https://lkml.kernel.org/r/20210311190845.9708-7-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Using kvfree_rcu() to free the old shrinker_maps instead of call_rcu().
We don't have to define a dedicated callback for call_rcu() anymore.

Link: https://lkml.kernel.org/r/20210311190845.9708-6-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but
actually the map size can be calculated via shrinker_nr_max, so it seems
unnecessary to keep both.  Remove memcg_shrinker_map_size since
shrinker_nr_max is also used by iterating the bit map.

Link: https://lkml.kernel.org/r/20210311190845.9708-5-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Since memcg_shrinker_map_size just can be changed under holding
shrinker_rwsem exclusively, the read side can be protected by holding read
lock, so it sounds superfluous to have a dedicated mutex.

Kirill Tkhai suggested use write lock since:

  * We want the assignment to shrinker_maps is visible for shrink_slab_memcg().
  * The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but
    in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing
    is not actually protected.
  * READ lock makes alloc_shrinker_info() racy against memory allocation fail.
    alloc_shrinker_info()->free_shrinker_info() may free memory right after
    shrink_slab_memcg() dereferenced it. You may say
    shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure,
    but this is not the thing we want to remember in the future, since this
    spreads modularity.

And a test with heavy paging workload didn't show write lock makes things worse.

Link: https://lkml.kernel.org/r/20210311190845.9708-4-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The shrinker map management is not purely memcg specific, it is at the
intersection between memory cgroup and shrinkers.  It's allocation and
assignment of a structure, and the only memcg bit is the map is being
stored in a memcg structure.  So move the shrinker_maps handling code
into vmscan.c for tighter integration with shrinker code, and remove the
"memcg_" prefix.  There is no functional change.

Link: https://lkml.kernel.org/r/20210311190845.9708-3-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Make shrinker's nr_deferred memcg aware", v10.

Recently huge amount one-off slab drop was seen on some vfs metadata
heavy workloads, it turned out there were huge amount accumulated
nr_deferred objects seen by the shrinker.

On our production machine, I saw absurd number of nr_deferred shown as
the below tracing result:

  <...>-48776 [032] .... 27970562.458916: mm_shrink_slab_start:
  super_cache_scan+0x0/0x1a0 ffff9a83046f3458: nid: 0 objects to shrink
  2531805877005 gfp_flags GFP_HIGHUSER_MOVABLE pgs_scanned 32 lru_pgs
  9300 cache items 1667 delta 11 total_scan 833

There are 2.5 trillion deferred objects on one node, assuming all of them
are dentry (192 bytes per object), so the total size of deferred on one
node is ~480TB.  It is definitely ridiculous.

I managed to reproduce this problem with kernel build workload plus
negative dentry generator.

First step, run the below kernel build test script:

NR_CPUS=`cat /proc/cpuinfo | grep -e processor | wc -l`

cd /root/Buildarea/linux-stable

for i in `seq 1500`; do
        cgcreate -g memory:kern_build
        echo 4G > /sys/fs/cgroup/memory/kern_build/memory.limit_in_bytes

        echo 3 > /proc/sys/vm/drop_caches
        cgexec -g memory:kern_build make clean > /dev/null 2>&1
        cgexec -g memory:kern_build make -j$NR_CPUS > /dev/null 2>&1

        cgdelete -g memory:kern_build
done

Then run the below negative dentry generator script:

NR_CPUS=`cat /proc/cpuinfo | grep -e processor | wc -l`

mkdir /sys/fs/cgroup/memory/test
echo $$ > /sys/fs/cgroup/memory/test/tasks

for i in `seq $NR_CPUS`; do
        while true; do
                FILE=`head /dev/urandom | tr -dc A-Za-z0-9 | head -c 64`
                cat $FILE 2>/dev/null
        done &
done

Then kswapd will shrink half of dentry cache in just one loop as the below
tracing result showed:

	kswapd0-475   [028] .... 305968.252561: mm_shrink_slab_start: super_cache_scan+0x0/0x190 0000000024acf00c: nid: 0 objects to shrink 4994376020 gfp_flags GFP_KERNEL cache items 93689873 delta 45746 total_scan 46844936 priority 12
	kswapd0-475   [021] .... 306013.099399: mm_shrink_slab_end: super_cache_scan+0x0/0x190 0000000024acf00c: nid: 0 unused scan count 4994376020 new scan count 4947576838 total_scan 8 last shrinker return val 46844928

There were huge number of deferred objects before the shrinker was called,
the behavior does match the code but it might be not desirable from the
user's stand of point.

The excessive amount of nr_deferred might be accumulated due to various
reasons, for example:

* GFP_NOFS allocation

* Significant times of small amount scan (< scan_batch, 1024 for vfs
  metadata)

However the LRUs of slabs are per memcg (memcg-aware shrinkers) but the
deferred objects is per shrinker, this may have some bad effects:

* Poor isolation among memcgs.  Some memcgs which happen to have
  frequent limit reclaim may get nr_deferred accumulated to a huge number,
  then other innocent memcgs may take the fall.  In our case the main
  workload was hit.

* Unbounded deferred objects.  There is no cap for deferred objects, it
  can outgrow ridiculously as the tracing result showed.

* Easy to get out of control.  Although shrinkers take into account
  deferred objects, but it can go out of control easily.  One
  misconfigured memcg could incur absurd amount of deferred objects in a
  period of time.

* Sort of reclaim problems, i.e.  over reclaim, long reclaim latency,
  etc.  There may be hundred GB slab caches for vfe metadata heavy
  workload, shrink half of them may take minutes.  We observed latency
  spike due to the prolonged reclaim.

These issues also have been discussed in
https://lore.kernel.org/linux-mm/20200916185823.5347-1-shy828301@gmail.com/.
The patchset is the outcome of that discussion.

So this patchset makes nr_deferred per-memcg to tackle the problem.  It
does:

* Have memcg_shrinker_deferred per memcg per node, just like what
  shrinker_map does.  Instead it is an atomic_long_t array, each element
  represent one shrinker even though the shrinker is not memcg aware, this
  simplifies the implementation.  For memcg aware shrinkers, the deferred
  objects are just accumulated to its own memcg.  The shrinkers just see
  nr_deferred from its own memcg.  Non memcg aware shrinkers still use
  global nr_deferred from struct shrinker.

* Once the memcg is offlined, its nr_deferred will be reparented to its
  parent along with LRUs.

* The root memcg has memcg_shrinker_deferred array too.  It simplifies
  the handling of reparenting to root memcg.

* Cap nr_deferred to 2x of the length of lru.  The idea is borrowed from
  Dave Chinner's series
  (https://lore.kernel.org/linux-xfs/20191031234618.15403-1-david@fromorbit.com/)

The downside is each memcg has to allocate extra memory to store the
nr_deferred array.  On our production environment, there are typically
around 40 shrinkers, so each memcg needs ~320 bytes.  10K memcgs would
need ~3.2MB memory.  It seems fine.

We have been running the patched kernel on some hosts of our fleet (test
and production) for months, it works very well.  The monitor data shows
the working set is sustained as expected.

This patch (of 13):

The tracepoint's nid should show what node the shrink happens on, the
start tracepoint uses nid from shrinkctl, but the nid might be set to 0
before end tracepoint if the shrinker is not NUMA aware, so the tracing
log may show the shrink happens on one node but end up on the other node.
It seems confusing.  And the following patch will remove using nid
directly in do_shrink_slab(), this patch also helps cleanup the code.

Link: https://lkml.kernel.org/r/20210311190845.9708-1-shy828301@gmail.com
Link: https://lkml.kernel.org/r/20210311190845.9708-2-shy828301@gmail.comSigned-off-by: NYang Shi <shy828301@gmail.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It is currently not obvious that the RECLAIM_* bits are part of the uapi
since they are defined in vmscan.c.  Move them to a uapi header to make it
obvious.

This should have no functional impact.

Link: https://lkml.kernel.org/r/20210219172557.08074910@viggo.jf.intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: NBen Widawsky <ben.widawsky@intel.com>
Reviewed-by: NOscar Salvador <osalvador@suse.de>
Acked-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Daniel Wagner <dwagner@suse.de>
Cc: "Tobin C. Harding" <tobin@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

alloc_contig_range() will fail if it finds a HugeTLB page within the
range, without a chance to handle them.  Since HugeTLB pages can be
migrated as any LRU or Movable page, it does not make sense to bail out
without trying.  Enable the interface to recognize in-use HugeTLB pages so
we can migrate them, and have much better chances to succeed the call.

Link: https://lkml.kernel.org/r/20210419075413.1064-7-osalvador@suse.deSigned-off-by: NOscar Salvador <osalvador@suse.de>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NDavid Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

I went to go add a new RECLAIM_* mode for the zone_reclaim_mode sysctl.
Like a good kernel developer, I also went to go update the
documentation.  I noticed that the bits in the documentation didn't
match the bits in the #defines.

The VM never explicitly checks the RECLAIM_ZONE bit.  The bit is,
however implicitly checked when checking 'node_reclaim_mode==0'.  The
RECLAIM_ZONE #define was removed in a cleanup.  That, by itself is fine.

But, when the bit was removed (bit 0) the _other_ bit locations also got
changed.  That's not OK because the bit values are documented to mean
one specific thing.  Users surely do not expect the meaning to change
from kernel to kernel.

The end result is that if someone had a script that did:

	sysctl vm.zone_reclaim_mode=1

it would have gone from enabling node reclaim for clean unmapped pages
to writing out pages during node reclaim after the commit in question.
That's not great.

Put the bits back the way they were and add a comment so something like
this is a bit harder to do again.  Update the documentation to make it
clear that the first bit is ignored.

Link: https://lkml.kernel.org/r/20210219172555.FF0CDF23@viggo.jf.intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
Fixes: 648b5cf3 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE")
Reviewed-by: NBen Widawsky <ben.widawsky@intel.com>
Reviewed-by: NOscar Salvador <osalvador@suse.de>
Acked-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Daniel Wagner <dwagner@suse.de>
Cc: "Tobin C. Harding" <tobin@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Qian Cai <cai@lca.pw>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

All other references to the function were removed after
commit b910718a ("mm: vmscan: detect file thrashing at the reclaim
root").

Link: https://lore.kernel.org/linux-mm/20201207220949.830352-11-yuzhao@google.com/
Link: https://lkml.kernel.org/r/20210122220600.906146-11-yuzhao@google.comSigned-off-by: NYu Zhao <yuzhao@google.com>
Reviewed-by: NAlex Shi <alex.shi@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>