to #26424368

Probe and calculate the latency of global swapout, memcg swapout and
swapin respectively, and then group into the latency histogram in struct
mem_cgroup.

Note that the latency in each memcg is aggregated from all child memcgs.

Usage:

$ cat memory.direct_swapout_global_latency
0-1ms:  98313
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      52

Each line is the count of global swapout within the appropriate latency
range.

To clear the latency histogram:

$ echo 0 > memory.direct_swapout_global_latency
$ cat memory.direct_swapout_global_latency
0-1ms:  0
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      0

The usage of memory.direct_swapout_memcg_latency and
memory.direct_swapin_latency is the same as
memory.direct_swapout_global_latency.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

to #26424368

There are some duplicate codes in the original implementation of memory
latency histogram, such as {x, y, z}_show, and {x, y, z}_write, where x,
y, z represents various types of memory latency.

This reworks common codes of memory latency histogram to make it easier
to add more types of memory latency later.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

to #26424368

Probe and calculate the latency of direct compact, and then group into
the latency histogram in struct mem_cgroup.

Note that the latency in each memcg is aggregated from all child memcgs.

Usage:

$ cat memory.direct_compact_latency
0-1ms:  1176
1-5ms:  259
5-10ms:         17
10-100ms:       10
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      921

Each line is the count of direct compact within the appropriate latency
range.

To clear the latency histogram:

$ echo 0 > memory.direct_compact_latency
$ cat memory.direct_compact_latency
0-1ms:  0
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      0
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

to #26424368

Probe and calculate the latency of global direct reclaim and memcg
direct reclaim, respectively, and then group into the latency histogram
in struct mem_cgroup. Besides, the total latency is accumulated each
time the histogram is updated.

Note that the latency in each memcg is aggregated from all child memcgs.

Usage:

$ cat memory.direct_reclaim_global_latency
0-1ms:  228
1-5ms:  283
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      539

Each line is the count of global direct reclaim within the appropriate
latency range.

To clear the latency histogram:

$ echo 0 > memory.direct_reclaim_global_latency
$ cat memory.direct_reclaim_global_latency
0-1ms:  0
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      0

The usage of memory.direct_reclaim_memcg_latency is the same as
memory.direct_reclaim_global_latency.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

The memcg background async page reclaim, a.k.a, memcg kswapd, is
implemented with a dedicated unbound workqueue currently.

However, memcg kswapd will run too frequently, resulting in high
overhead, page cache thrashing, frequent dirty page writeback, etc., due
to improper memcg memory.wmark_ratio, unreasonable memcg memor capacity,
or even abnormal memcg memory usage.

We need to find out the problematic memcg(s) where memcg kswapd
introduces significant overhead.

This records the latency of each run of memcg kswapd work, and then
aggregates into the exstat of per memcg.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

Under memory pressure reclaim and oom would happen, with multiple
cgroups exist in one system, we might want some of their memory
or tasks survived the reclaim and oom while there are other
candidates.

The @memory.low and @memory.min have make that happen during reclaim,
this patch introduces memcg priority oom to meet above requirement in
the oom.

The priority is from 0 to 12, the higher number the higher priority.
When oom happens it always choose victim from low priority memcg.
And it works both for memcg oom and global oom, it can be enabled/disabled
through @memory.use_priority_oom, for global oom through the root
memcg's @memory.use_priority_oom, it is disabled by default.
Signed-off-by: NWenwei Tao <wenwei.tao@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

Accessing original memory.stat turned out to be one heavy
operation which has been caused many real product problems.

Introduce new cgroup memory.exstat, memory.exstat stands
for "extra/extended memory.stat", which contains dedicated
statistics from Alibaba Clould Kernel.

memory.exstat is supposed to provide hierarchical statistics.

Export its first "wmark_min_throttled_ms", and will add more
like direct reclaim, direct compaction, etc.
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>

In co-location environment, there are more or less some memory
overcommitment, then BATCH tasks may break the shared global min
watermark resulting in all types of applications falling into
the direct reclaim slow path hurting the RT of LS tasks.
(NOTE: BATCH tasks tolerate big latency spike even in seconds
as long as doesn't hurt its overal throughput. While LS tasks
are very Latency-Sensitive, they may time out or fail in case
of sudden latency spike lasts like hundreds of ms typically.)

Actually BATCH tasks are not sensitive to memory latency, they
can be assigned a strict min watermark which is different from
that of LS tasks(which can be aissgned a lenient min watermark
accordingly), thus isolating each other in case of global memory
allocation. This is kind of like the idea behind ALLOC_HARDER
for rt_task(), see gfp_to_alloc_flags().

memory.wmark_min_adj stands for memcg global WMARK_MIN adjustment,
it is used to realize separate min watermarks above-mentioned for
memcgs, its valid value is within [-25, 50], specifically:
negative value means to be relative to [0, WMARK_MIN],
positive value means to be relative to [WMARK_MIN, WMARK_LOW].
For examples,
  -25 means "WMARK_MIN + (WMARK_MIN - 0) * (-25%)"
   50 means "WMARK_MIN + (WMARK_LOW - WMARK_MIN) * 50%"

Note that the minimum -25 is what ALLOC_HARDER uses which is safe
for us to adopt, and the maximum 50 is one experienced value.

Negative memory.wmark_min_adj means high QoS requirements, it can
allocate below the global WMARK_MIN, which is kind of like the idea
behind ALLOC_HARDER, see gfp_to_alloc_flags().

Positive memory.wmark_min_adj means low QoS requirements, thus when
allocation broke memcg min watermark, it should trigger direct reclaim
traditionally, and we trigger throttle instead to further prevent
them from disturbing others.

With this interface, we can assign positive values for BATCH memcgs
and negative values for LS memcgs.

memory.wmark_min_adj default value is 0, and inherit from its parent,
Note that the final effective wmark_min_adj will consider all the
hierarchical values, its value is the maximal(most conservative)
wmark_min_adj along the hierarchy but excluding intermediate default
values(zero).
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>

After memcg was deleted, page caches still reference to this memcg
causing large number of dead(zombie) memcgs in the system. Then it
slows down access to "/sys/fs/cgroup/cpu/memory.stat", etc due to
tons of iterations, further causing various latencies.

This patch introduces two ways to reclaim these zombie memcgs.
1) Background kthread reaper
Introduce a kernel thread "memcg_zombie_reaper" to reclaim zombie
memcgs at background periodically.

Several knobs are also added to control the reaper scan frequency:
- /sys/kernel/mm/memcg_reaper/scan_interval
  The scan period in second. Default 5s.
- /sys/kernel/mm/memcg_reaper/pages_scan
  The scan rate of pages per scan. Default 1310720(5GiB for 4KiB page).
- /sys/kernel/mm/memcg_reaper/verbose
  Output some zombie memcg information for debug purpose. Default off.
- /sys/kernel/mm/memcg_reaper/reap_background
  "on/off" switch. Default "0" means off. Write "1" to switch it on.

2) One-shot trigger by users
- /sys/kernel/mm/memcg_reaper/reap
  Write "1" to trigger one round of zombie memcg reaping, but without
  any guarantee, you may need to launch multiple rounds as needed.
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>

commit 1e577f970f66a53d429cbee37b36177c9712f488 upstream.

The memory controller in cgroup v2 exposes memory.events file for each
memcg which shows the number of times events like low, high, max, oom
and oom_kill have happened for the whole tree rooted at that memcg.
Users can also poll or register notification to monitor the changes in
that file.  Any event at any level of the tree rooted at memcg will
notify all the listeners along the path till root_mem_cgroup.  There are
existing users which depend on this behavior.

However there are users which are only interested in the events
happening at a specific level of the memcg tree and not in the events in
the underlying tree rooted at that memcg.  One such use-case is a
centralized resource monitor which can dynamically adjust the limits of
the jobs running on a system.  The jobs can create their sub-hierarchy
for their own sub-tasks.  The centralized monitor is only interested in
the events at the top level memcgs of the jobs as it can then act and
adjust the limits of the jobs.  Using the current memory.events for such
centralized monitor is very inconvenient.  The monitor will keep
receiving events which it is not interested and to find if the received
event is interesting, it has to read memory.event files of the next
level and compare it with the top level one.  So, let's introduce
memory.events.local to the memcg which shows and notify for the events
at the memcg level.

Now, does memory.stat and memory.pressure need their local versions.  IMHO
no due to the no internal process contraint of the cgroup v2.  The
memory.stat file of the top level memcg of a job shows the stats and
vmevents of the whole tree.  The local stats or vmevents of the top level
memcg will only change if there is a process running in that memcg but v2
does not allow that.  Similarly for memory.pressure there will not be any
process in the internal nodes and thus no chance of local pressure.

Link: http://lkml.kernel.org/r/20190527174643.209172-1-shakeelb@google.comSigned-off-by: NShakeel Butt <shakeelb@google.com>
Reviewed-by: NRoman Gushchin <guro@fb.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Chris Down <chris@chrisdown.name>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

commit 9852ae3fe5293264f01c49f2571ef7688f7823ce upstream.

memory.stat and other files already consider subtrees in their output, and
we should too in order to not present an inconsistent interface.

The current situation is fairly confusing, because people interacting with
cgroups expect hierarchical behaviour in the vein of memory.stat,
cgroup.events, and other files.  For example, this causes confusion when
debugging reclaim events under low, as currently these always read "0" at
non-leaf memcg nodes, which frequently causes people to misdiagnose breach
behaviour.  The same confusion applies to other counters in this file when
debugging issues.

Aggregation is done at write time instead of at read-time since these
counters aren't hot (unlike memory.stat which is per-page, so it does it
at read time), and it makes sense to bundle this with the file
notifications.

After this patch, events are propagated up the hierarchy:

    [root@ktst ~]# cat /sys/fs/cgroup/system.slice/memory.events
    low 0
    high 0
    max 0
    oom 0
    oom_kill 0
    [root@ktst ~]# systemd-run -p MemoryMax=1 true
    Running as unit: run-r251162a189fb4562b9dabfdc9b0422f5.service
    [root@ktst ~]# cat /sys/fs/cgroup/system.slice/memory.events
    low 0
    high 0
    max 7
    oom 1
    oom_kill 1

As this is a change in behaviour, this can be reverted to the old
behaviour by mounting with the `memory_localevents' flag set.  However, we
use the new behaviour by default as there's a lack of evidence that there
are any current users of memory.events that would find this change
undesirable.

akpm: this is a behaviour change, so Cc:stable.  THis is so that
forthcoming distros which use cgroup v2 are more likely to pick up the
revised behaviour.

[xuyu: remove the new memory_localevents mount option because it is
rarely used]

Link: http://lkml.kernel.org/r/20190208224419.GA24772@chrisdown.nameSigned-off-by: NChris Down <chris@chrisdown.name>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

We reserve some fields beforehand for core structures prone to change,
so that we won't hurt when extra fields have to be added for hotfix,
thereby inceasing the success rate, we even can hot add features with
this enhancement.

After reserving, normally cache does not matter as the reserved fields
(usually at tail) are not accessed at all.

Currently involve the following structures:
    MM:
    struct zone
    struct pglist_data
    struct mm_struct
    struct vm_area_struct
    struct mem_cgroup
    struct writeback_control

    Block:
    struct gendisk
    struct backing_dev_info
    struct bio
    struct queue_limits
    struct request_queue
    struct blkcg
    struct blkcg_policy
    struct blk_mq_hw_ctx
    struct blk_mq_tag_set
    struct blk_mq_queue_data
    struct blk_mq_ops
    struct elevator_mq_ops
    struct inode
    struct dentry
    struct address_space
    struct block_device
    struct hd_struct
    struct bio_set

    Network:
    struct sk_buff
    struct sock
    struct net_device_ops
    struct xt_target
    struct dst_entry
    struct dst_ops
    struct fib_rule

    Scheduler:
    struct task_struct
    struct cfs_rq
    struct rq
    struct sched_statistics
    struct sched_entity
    struct signal_struct
    struct task_group
    struct cpuacct

    cgroup:
    struct cgroup_root
    struct cgroup_subsys_state
    struct cgroup_subsys
    struct css_set
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>
[ caspar: use SPDX-License-Identifier ]
Signed-off-by: NCaspar Zhang <caspar@linux.alibaba.com>

The commit 87eaceb3faa59b9b4d940ec9554ce251325d83fe ("mm: thp: make
deferred split shrinker memcg aware") makes deferred split queue per
memcg to resolve memcg pre-mature OOM problem.  But, all nodes end up
sharing the same queue instead of one queue per-node before the commit.
It is not a big deal for memcg limit reclaim, but it may cause global
kswapd shrink THPs from a different node.

And, 0-day testing reported -19.6% regression of stress-ng's madvise
test [1].  I didn't see that much regression on my test box (24 threads,
48GB memory, 2 nodes), with the same test (stress-ng --timeout 1
--metrics-brief --sequential 72  --class vm --exclude spawn,exec), I saw
average -3% (run the same test 10 times then calculate the average since
the test itself may have most 15% variation according to my test)
regression sometimes (not every time, sometimes I didn't see regression
at all).

This might be caused by deferred split queue lock contention.  With some
configuration (i.e. just one root memcg) the lock contention my be worse
than before (given 2 nodes, two locks are reduced to one lock).

So, moving deferred split queue to memcg's nodeinfo to make it NUMA
aware again.

With this change stress-ng's madvise test shows average 4% improvement
sometimes and I didn't see degradation anymore.

[1]: https://lore.kernel.org/lkml/20190930084604.GC17687@shao2-debian/

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

commit 87eaceb3faa59b9b4d940ec9554ce251325d83fe upstream

Currently THP deferred split shrinker is not memcg aware, this may cause
premature OOM with some configuration.  For example the below test would
run into premature OOM easily:

$ cgcreate -g memory:thp
$ echo 4G > /sys/fs/cgroup/memory/thp/memory/limit_in_bytes
$ cgexec -g memory:thp transhuge-stress 4000

transhuge-stress comes from kernel selftest.

It is easy to hit OOM, but there are still a lot THP on the deferred
split queue, memcg direct reclaim can't touch them since the deferred split
shrinker is not memcg aware.

Convert deferred split shrinker memcg aware by introducing per memcg
deferred split queue.  The THP should be on either per node or per memcg
deferred split queue if it belongs to a memcg.  When the page is
immigrated to the other memcg, it will be immigrated to the target
memcg's deferred split queue too.

Reuse the second tail page's deferred_list for per memcg list since the
same THP can't be on multiple deferred split queues.

[yang.shi@linux.alibaba.com: simplify deferred split queue dereference per Kirill Tkhai]
  Link: http://lkml.kernel.org/r/1566496227-84952-5-git-send-email-yang.shi@linux.alibaba.com
Link: http://lkml.kernel.org/r/1565144277-36240-5-git-send-email-yang.shi@linux.alibaba.comSigned-off-by: NYang Shi <yang.shi@linux.alibaba.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 upstream

Currently shrinker is just allocated and can work when memcg kmem is
enabled.  But, THP deferred split shrinker is not slab shrinker, it
doesn't make too much sense to have such shrinker depend on memcg kmem.
It should be able to reclaim THP even though memcg kmem is disabled.

Introduce a new shrinker flag, SHRINKER_NONSLAB, for non-slab shrinker.
When memcg kmem is disabled, just such shrinkers can be called in
shrinking memcg slab.

[yang.shi@linux.alibaba.com: add comment]
  Link: http://lkml.kernel.org/r/1566496227-84952-4-git-send-email-yang.shi@linux.alibaba.com
Link: http://lkml.kernel.org/r/1565144277-36240-4-git-send-email-yang.shi@linux.alibaba.comSigned-off-by: NYang Shi <yang.shi@linux.alibaba.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

This enables scanning pages in fixed interval to determine their access
frequency (hot/cold). The result is exported to user land on basis of
memory cgroup by "memory.idle_page_stats". The design is highlighted as
below:

   * A kernel thread is spawn when this feature is enabled by writing
     non-zero value to "/sys/kernel/mm/kidled/scan_period_in_seconds".
     The thread sequentially scans the nodes and their pages that have
     been chained up in LRU list.

   * For each page, its corresponding age information is stored in the
     page flags or array in node. The age represents the scanning intervals
     in which the page isn't accessed. Also, the page flag (PG_idle) is
     leveraged. The page's age is increased by one if the idle flag isn't
     cleared in two consective scans. Otherwise, the page's age is cleared out.
     Also, the page's age information is cleared when it's free'd so that
     the stale age information won't be fetched when it's allocated.

   * Initially, the flag is set, while the access bit in its PTE is cleared
     out by the thread. In next scanning period, its PTE access bit is
     synchronized with the page flag: clear the flag if access bit is set.
     The flag is kept otherwise. For unmapped pages, the flag is cleared
     when it's accessed.

   * Eventually, the page's aging information is updated to the unstable
     bucket of its corresponding memory cgroup, taking as statistics. The
     unstable bucket (statistics) is copied to stable bucket when all pages
     in all nodes are scanned for once. The stable bucket (statistics) is
     exported to user land through "memory.idle_page_stats".

TESTING
=======

   * cgroup1, unmapped pagecache

     # dd if=/dev/zero of=/ext4/test.data oflag=direct bs=1M count=128
     #
     # echo 1 > /sys/kernel/mm/kidled/use_hierarchy
     # echo 15 > /sys/kernel/mm/kidled/scan_period_in_seconds
     # mkdir -p /cgroup/memory
     # mount -tcgroup -o memory /cgroup/memory
     # echo 1 > /cgroup/memory/memory.use_hierarchy
     # mkdir -p /cgroup/memory/test
     # echo 1 > /cgroup/memory/test/memory.use_hierarchy
     #
     # echo $$ > /cgroup/memory/test/cgroup.procs
     # dd if=/ext4/test.data of=/dev/null bs=1M count=128
     # < wait a few minutes >
     # cat /cgroup/memory/test/memory.idle_page_stats | grep cfei
     # cat /cgroup/memory/test/memory.idle_page_stats | grep cfei
       cfei   0   0   0   134217728   0   0   0   0
     # cat /cgroup/memory/memory.idle_page_stats | grep cfei
       cfei   0   0   0   134217728   0   0   0   0

   * cgroup1, mapped pagecache

     # < create same file and memory cgroups as above >
     #
     # echo $$ > /cgroup/memory/test/cgroup.procs
     # < run program to mmap the whole created file and access the area >
     # < wait a few minutes >
     # cat /cgroup/memory/test/memory.idle_page_stats | grep cfei
       cfei   0   134217728   0   0   0   0   0   0
     # cat /cgroup/memory/memory.idle_page_stats | grep cfei
       cfei   0   134217728   0   0   0   0   0   0

   * cgroup1, mapped and locked pagecache

     # < create same file and memory cgroups as above >
     #
     # echo $$ > /cgroup/memory/test/cgroup.procs
     # < run program to mmap the whole created file and mlock the area >
     # < wait a few minutes >
     # cat /cgroup/memory/test/memory.idle_page_stats | grep cfui
       cfui   0   134217728   0   0   0   0   0   0
     # cat /cgroup/memory/memory.idle_page_stats | grep cfui
       cfui   0   134217728   0   0   0   0   0   0

   * cgroup1, anonymous and locked area

     # < create memory cgroups as above >
     #
     # echo $$ > /cgroup/memory/test/cgroup.procs
     # < run program to mmap anonymous area and mlock it >
     # < wait a few minutes >
     # cat /cgroup/memory/test/memory.idle_page_stats | grep csui
       csui   0   0   134217728   0   0   0   0   0
     # cat /cgroup/memory/memory.idle_page_stats | grep csui
       csui   0   0   134217728   0   0   0   0   0

   * Rerun above test cases in cgroup2 and the results are no exceptional.
     However, the cgroups are populated in different way as below:

     # mkdir -p /cgroup
     # mount -tcgroup2 none /cgroup
     # echo "+memory" > /cgroup/cgroup.subtree_control
     # mkdir -p /cgroup/test
Signed-off-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

Introduce a new interface, wmark_scale_factor, which defines the
distance between wmark_high and wmark_low.  The unit is in fractions of
10,000. The default value of 50 means the distance between wmark_high
and wmark_low is 0.5% of the max limit of the cgroup.  The maximum value
is 1000, or 10% of the max limit.

The distance between wmark_low and wmark_high have impact on how hard
memcg kswapd would reclaim.
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: NYang Shi <yang.shi@linux.alibaba.com>

The global kswapd could set memory node to dirty or writeback if current
scan find all pages are unqueued dirty or writeback.  Then kswapd would
write out dirty pages or wait for writeback done.  The memcg kswapd
behaves like global kswapd, and it should set dirty or writeback state
to memcg too if the same condition is met.

Since direct reclaim can't write out page caches, the system depends on
kswapd to write out dirty pages if scan finds too many dirty pages in
order to avoid pre-mature OOM.  But, if page cache is dirtied too fast,
writing out pages definitely can't catch up with dirtying pages.  It is
the responsibility of dirty page balance to throttle dirtying pages.
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: NYang Shi <yang.shi@linux.alibaba.com>

Currently when memory usage exceeds memory cgroup limit, memory cgroup
just can do sync direct reclaim.  This may incur unexpected stall on
some applications which are sensitive to latency.  Introduce background
async page reclaim mechanism, like what kswapd does.

Define memcg memory usage water mark by introducing wmark_ratio interface,
which is from 0 to 100 and represents percentage of max limit.  The
wmark_high is calculated by (max * wmark_ratio / 100), the wmark_low is
(wmark_high - wmark_high >> 8), which is an empirical value.  If wmark_ratio
is 0, it means water mark is disabled, both wmark_low and wmark_high is max,
which is the default value.

If wmark_ratio is setup, when charging page, if usage is greater than
wmark_high, which means the available memory of memcg is low, a work
would be scheduled to do background page reclaim until memory usage is
reduced to wmark_low if possible.

Define a dedicated unbound workqueue for scheduling water mark reclaim
works.
Reviewed-by: NGavin Shan <shan.gavin@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: NYang Shi <yang.shi@linux.alibaba.com>

commit 0b3d6e6f2dd0a7b697b1aa8c167265908940624b upstream.

Since commit a983b5eb ("mm: memcontrol: fix excessive complexity in
memory.stat reporting") memcg dirty and writeback counters are managed
as:

 1) per-memcg per-cpu values in range of [-32..32]

 2) per-memcg atomic counter

When a per-cpu counter cannot fit in [-32..32] it's flushed to the
atomic.  Stat readers only check the atomic.  Thus readers such as
balance_dirty_pages() may see a nontrivial error margin: 32 pages per
cpu.

Assuming 100 cpus:
   4k x86 page_size:  13 MiB error per memcg
  64k ppc page_size: 200 MiB error per memcg

Considering that dirty+writeback are used together for some decisions the
errors double.

This inaccuracy can lead to undeserved oom kills.  One nasty case is
when all per-cpu counters hold positive values offsetting an atomic
negative value (i.e.  per_cpu[*]=32, atomic=n_cpu*-32).
balance_dirty_pages() only consults the atomic and does not consider
throttling the next n_cpu*32 dirty pages.  If the file_lru is in the
13..200 MiB range then there's absolutely no dirty throttling, which
burdens vmscan with only dirty+writeback pages thus resorting to oom
kill.

It could be argued that tiny containers are not supported, but it's more
subtle.  It's the amount the space available for file lru that matters.
If a container has memory.max-200MiB of non reclaimable memory, then it
will also suffer such oom kills on a 100 cpu machine.

The following test reliably ooms without this patch.  This patch avoids
oom kills.

  $ cat test
  mount -t cgroup2 none /dev/cgroup
  cd /dev/cgroup
  echo +io +memory > cgroup.subtree_control
  mkdir test
  cd test
  echo 10M > memory.max
  (echo $BASHPID > cgroup.procs && exec /memcg-writeback-stress /foo)
  (echo $BASHPID > cgroup.procs && exec dd if=/dev/zero of=/foo bs=2M count=100)

  $ cat memcg-writeback-stress.c
  /*
   * Dirty pages from all but one cpu.
   * Clean pages from the non dirtying cpu.
   * This is to stress per cpu counter imbalance.
   * On a 100 cpu machine:
   * - per memcg per cpu dirty count is 32 pages for each of 99 cpus
   * - per memcg atomic is -99*32 pages
   * - thus the complete dirty limit: sum of all counters 0
   * - balance_dirty_pages() only sees atomic count -99*32 pages, which
   *   it max()s to 0.
   * - So a workload can dirty -99*32 pages before balance_dirty_pages()
   *   cares.
   */
  #define _GNU_SOURCE
  #include <err.h>
  #include <fcntl.h>
  #include <sched.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <sys/stat.h>
  #include <sys/sysinfo.h>
  #include <sys/types.h>
  #include <unistd.h>

  static char *buf;
  static int bufSize;

  static void set_affinity(int cpu)
  {
  	cpu_set_t affinity;

  	CPU_ZERO(&affinity);
  	CPU_SET(cpu, &affinity);
  	if (sched_setaffinity(0, sizeof(affinity), &affinity))
  		err(1, "sched_setaffinity");
  }

  static void dirty_on(int output_fd, int cpu)
  {
  	int i, wrote;

  	set_affinity(cpu);
  	for (i = 0; i < 32; i++) {
  		for (wrote = 0; wrote < bufSize; ) {
  			int ret = write(output_fd, buf+wrote, bufSize-wrote);
  			if (ret == -1)
  				err(1, "write");
  			wrote += ret;
  		}
  	}
  }

  int main(int argc, char **argv)
  {
  	int cpu, flush_cpu = 1, output_fd;
  	const char *output;

  	if (argc != 2)
  		errx(1, "usage: output_file");

  	output = argv[1];
  	bufSize = getpagesize();
  	buf = malloc(getpagesize());
  	if (buf == NULL)
  		errx(1, "malloc failed");

  	output_fd = open(output, O_CREAT|O_RDWR);
  	if (output_fd == -1)
  		err(1, "open(%s)", output);

  	for (cpu = 0; cpu < get_nprocs(); cpu++) {
  		if (cpu != flush_cpu)
  			dirty_on(output_fd, cpu);
  	}

  	set_affinity(flush_cpu);
  	if (fsync(output_fd))
  		err(1, "fsync(%s)", output);
  	if (close(output_fd))
  		err(1, "close(%s)", output);
  	free(buf);
  }

Make balance_dirty_pages() and wb_over_bg_thresh() work harder to
collect exact per memcg counters.  This avoids the aforementioned oom
kills.

This does not affect the overhead of memory.stat, which still reads the
single atomic counter.

Why not use percpu_counter? memcg already handles cpus going offline, so
no need for that overhead from percpu_counter.  And the percpu_counter
spinlocks are more heavyweight than is required.

It probably also makes sense to use exact dirty and writeback counters
in memcg oom reports.  But that is saved for later.

Link: http://lkml.kernel.org/r/20190329174609.164344-1-gthelen@google.comSigned-off-by: NGreg Thelen <gthelen@google.com>
Reviewed-by: NRoman Gushchin <guro@fb.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>	[4.16+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

For some workloads an intervention from the OOM killer can be painful.
Killing a random task can bring the workload into an inconsistent state.

Historically, there are two common solutions for this
problem:
1) enabling panic_on_oom,
2) using a userspace daemon to monitor OOMs and kill
   all outstanding processes.

Both approaches have their downsides: rebooting on each OOM is an obvious
waste of capacity, and handling all in userspace is tricky and requires a
userspace agent, which will monitor all cgroups for OOMs.

In most cases an in-kernel after-OOM cleaning-up mechanism can eliminate
the necessity of enabling panic_on_oom.  Also, it can simplify the cgroup
management for userspace applications.

This commit introduces a new knob for cgroup v2 memory controller:
memory.oom.group.  The knob determines whether the cgroup should be
treated as an indivisible workload by the OOM killer.  If set, all tasks
belonging to the cgroup or to its descendants (if the memory cgroup is not
a leaf cgroup) are killed together or not at all.

To determine which cgroup has to be killed, we do traverse the cgroup
hierarchy from the victim task's cgroup up to the OOMing cgroup (or root)
and looking for the highest-level cgroup with memory.oom.group set.

Tasks with the OOM protection (oom_score_adj set to -1000) are treated as
an exception and are never killed.

This patch doesn't change the OOM victim selection algorithm.

Link: http://lkml.kernel.org/r/20180802003201.817-4-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce set_shrinker_bit() function to set shrinker-related bit in
memcg shrinker bitmap, and set the bit after the first item is added and
in case of reparenting destroyed memcg's items.

This will allow next patch to make shrinkers be called only, in case of
they have charged objects at the moment, and to improve shrink_slab()
performance.

[ktkhai@virtuozzo.com: v9]
  Link: http://lkml.kernel.org/r/153112557572.4097.17315791419810749985.stgit@localhost.localdomain
Link: http://lkml.kernel.org/r/153063065671.1818.15914674956134687268.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: NShakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This will be used in next patch.

Link: http://lkml.kernel.org/r/153063064347.1818.1987011484100392706.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: NShakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Imagine a big node with many cpus, memory cgroups and containers.  Let
we have 200 containers, every container has 10 mounts, and 10 cgroups.
All container tasks don't touch foreign containers mounts.  If there is
intensive pages write, and global reclaim happens, a writing task has to
iterate over all memcgs to shrink slab, before it's able to go to
shrink_page_list().

Iteration over all the memcg slabs is very expensive: the task has to
visit 200 * 10 = 2000 shrinkers for every memcg, and since there are
2000 memcgs, the total calls are 2000 * 2000 = 4000000.

So, the shrinker makes 4 million do_shrink_slab() calls just to try to
isolate SWAP_CLUSTER_MAX pages in one of the actively writing memcg via
shrink_page_list().  I've observed a node spending almost 100% in
kernel, making useless iteration over already shrinked slab.

This patch adds bitmap of memcg-aware shrinkers to memcg.  The size of
the bitmap depends on bitmap_nr_ids, and during memcg life it's
maintained to be enough to fit bitmap_nr_ids shrinkers.  Every bit in
the map is related to corresponding shrinker id.

Next patches will maintain set bit only for really charged memcg.  This
will allow shrink_slab() to increase its performance in significant way.
See the last patch for the numbers.

[ktkhai@virtuozzo.com: v9]
  Link: http://lkml.kernel.org/r/153112549031.4097.3576147070498769979.stgit@localhost.localdomain
[ktkhai@virtuozzo.com: add comment to mem_cgroup_css_online()]
  Link: http://lkml.kernel.org/r/521f9e5f-c436-b388-fe83-4dc870bfb489@virtuozzo.com
Link: http://lkml.kernel.org/r/153063056619.1818.12550500883688681076.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: NShakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce new config option, which is used to replace repeating
CONFIG_MEMCG && !CONFIG_SLOB pattern.  Next patches add a little more
memcg+kmem related code, so let's keep the defines more clearly.

Link: http://lkml.kernel.org/r/153063053670.1818.15013136946600481138.stgit@localhost.localdomainSigned-off-by: NKirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: NVladimir Davydov <vdavydov.dev@gmail.com>
Tested-by: NShakeel Butt <shakeelb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Sahitya Tummala <stummala@codeaurora.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 3812c8c8 ("mm: memcg: do not trap chargers with full
callstack on OOM") has changed the ENOMEM semantic of memcg charges.
Rather than invoking the oom killer from the charging context it delays
the oom killer to the page fault path (pagefault_out_of_memory).  This
in turn means that many users (e.g.  slab or g-u-p) will get ENOMEM when
the corresponding memcg hits the hard limit and the memcg is is OOM.
This is behavior is inconsistent with !memcg case where the oom killer
is invoked from the allocation context and the allocator keeps retrying
until it succeeds.

The difference in the behavior is user visible.  mmap(MAP_POPULATE)
might result in not fully populated ranges while the mmap return code
doesn't tell that to the userspace.  Random syscalls might fail with
ENOMEM etc.

The primary motivation of the different memcg oom semantic was the
deadlock avoidance.  Things have changed since then, though.  We have an
async oom teardown by the oom reaper now and so we do not have to rely
on the victim to tear down its memory anymore.  Therefore we can return
to the original semantic as long as the memcg oom killer is not handed
over to the users space.

There is still one thing to be careful about here though.  If the oom
killer is not able to make any forward progress - e.g.  because there is
no eligible task to kill - then we have to bail out of the charge path
to prevent from same class of deadlocks.  We have basically two options
here.  Either we fail the charge with ENOMEM or force the charge and
allow overcharge.  The first option has been considered more harmful
than useful because rare inconsistencies in the ENOMEM behavior is hard
to test for and error prone.  Basically the same reason why the page
allocator doesn't fail allocations under such conditions.  The later
might allow runaways but those should be really unlikely unless somebody
misconfigures the system.  E.g.  allowing to migrate tasks away from the
memcg to a different unlimited memcg with move_charge_at_immigrate
disabled.

Link: http://lkml.kernel.org/r/20180628151101.25307-1-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NGreg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The buffer_head can consume a significant amount of system memory and is
directly related to the amount of page cache.  In our production
environment we have observed that a lot of machines are spending a
significant amount of memory as buffer_head and can not be left as
system memory overhead.

Charging buffer_head is not as simple as adding __GFP_ACCOUNT to the
allocation.  The buffer_heads can be allocated in a memcg different from
the memcg of the page for which buffer_heads are being allocated.  One
concrete example is memory reclaim.  The reclaim can trigger I/O of
pages of any memcg on the system.  So, the right way to charge
buffer_head is to extract the memcg from the page for which buffer_heads
are being allocated and then use targeted memcg charging API.

[shakeelb@google.com: use __GFP_ACCOUNT for directed memcg charging]
  Link: http://lkml.kernel.org/r/20180702220208.213380-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180627191250.209150-3-shakeelb@google.comSigned-off-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Directed kmem charging", v8.

The Linux kernel's memory cgroup allows limiting the memory usage of the
jobs running on the system to provide isolation between the jobs.  All
the kernel memory allocated in the context of the job and marked with
__GFP_ACCOUNT will also be included in the memory usage and be limited
by the job's limit.

The kernel memory can only be charged to the memcg of the process in
whose context kernel memory was allocated.  However there are cases
where the allocated kernel memory should be charged to the memcg
different from the current processes's memcg.  This patch series
contains two such concrete use-cases i.e.  fsnotify and buffer_head.

The fsnotify event objects can consume a lot of system memory for large
or unlimited queues if there is either no or slow listener.  The events
are allocated in the context of the event producer.  However they should
be charged to the event consumer.  Similarly the buffer_head objects can
be allocated in a memcg different from the memcg of the page for which
buffer_head objects are being allocated.

To solve this issue, this patch series introduces mechanism to charge
kernel memory to a given memcg.  In case of fsnotify events, the memcg
of the consumer can be used for charging and for buffer_head, the memcg
of the page can be charged.  For directed charging, the caller can use
the scope API memalloc_[un]use_memcg() to specify the memcg to charge
for all the __GFP_ACCOUNT allocations within the scope.

This patch (of 2):

A lot of memory can be consumed by the events generated for the huge or
unlimited queues if there is either no or slow listener.  This can cause
system level memory pressure or OOMs.  So, it's better to account the
fsnotify kmem caches to the memcg of the listener.

However the listener can be in a different memcg than the memcg of the
producer and these allocations happen in the context of the event
producer.  This patch introduces remote memcg charging API which the
producer can use to charge the allocations to the memcg of the listener.

There are seven fsnotify kmem caches and among them allocations from
dnotify_struct_cache, dnotify_mark_cache, fanotify_mark_cache and
inotify_inode_mark_cachep happens in the context of syscall from the
listener.  So, SLAB_ACCOUNT is enough for these caches.

The objects from fsnotify_mark_connector_cachep are not accounted as
they are small compared to the notification mark or events and it is
unclear whom to account connector to since it is shared by all events
attached to the inode.

The allocations from the event caches happen in the context of the event
producer.  For such caches we will need to remote charge the allocations
to the listener's memcg.  Thus we save the memcg reference in the
fsnotify_group structure of the listener.

This patch has also moved the members of fsnotify_group to keep the size
same, at least for 64 bit build, even with additional member by filling
the holes.

[shakeelb@google.com: use GFP_KERNEL_ACCOUNT rather than open-coding it]
  Link: http://lkml.kernel.org/r/20180702215439.211597-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180627191250.209150-2-shakeelb@google.comSigned-off-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce the mem_cgroup_put() helper, which helps to eliminate guarding
memcg css release with "#ifdef CONFIG_MEMCG" in multiple places.

Link: http://lkml.kernel.org/r/20180623000600.5818-2-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@kernel.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Memory allocations can induce swapping via kswapd or direct reclaim.  If
we are having IO done for us by kswapd and don't actually go into direct
reclaim we may never get scheduled for throttling.  So instead check to
see if our cgroup is congested, and if so schedule the throttling.
Before we return to user space the throttling stuff will only throttle
if we actually required it.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Commit e27be240 ("mm: memcg: make sure memory.events is uptodate
when waking pollers") converted most of memcg event counters to
per-memcg atomics, which made them less confusing for a user.  The
"oom_kill" counter remained untouched, so now it behaves differently
than other counters (including "oom").  This adds nothing but confusion.

Let's fix this by adding the MEMCG_OOM_KILL event, and follow the
MEMCG_OOM approach.

This also removes a hack from count_memcg_event_mm(), introduced earlier
specially for the OOM_KILL counter.

[akpm@linux-foundation.org: fix for droppage of memcg-replace-mm-owner-with-mm-memcg.patch]
Link: http://lkml.kernel.org/r/20180508124637.29984-1-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The LKP robot found a 27% will-it-scale/page_fault3 performance
regression regarding commit e27be240("mm: memcg: make sure
memory.events is uptodate when waking pollers").

What the test does is:
 1 mkstemp() a 128M file on a tmpfs;
 2 start $nr_cpu processes, each to loop the following:
   2.1 mmap() this file in shared write mode;
   2.2 write 0 to this file in a PAGE_SIZE step till the end of the file;
   2.3 unmap() this file and repeat this process.
 3 After 5 minutes, check how many loops they managed to complete, the
   higher the better.

The commit itself looks innocent enough as it merely changed some event
counting mechanism and this test didn't trigger those events at all.
Perf shows increased cycles spent on accessing root_mem_cgroup->stat_cpu
in count_memcg_event_mm()(called by handle_mm_fault()) and in
__mod_memcg_state() called by page_add_file_rmap().  So it's likely due
to the changed layout of 'struct mem_cgroup' that either make stat_cpu
falling into a constantly modifying cacheline or some hot fields stop
being in the same cacheline.

I verified this by moving memory_events[] back to where it was:

: --- a/include/linux/memcontrol.h
: +++ b/include/linux/memcontrol.h
: @@ -205,7 +205,6 @@ struct mem_cgroup {
:  	int		oom_kill_disable;
:
:  	/* memory.events */
: -	atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS];
:  	struct cgroup_file events_file;
:
:  	/* protect arrays of thresholds */
: @@ -238,6 +237,7 @@ struct mem_cgroup {
:  	struct mem_cgroup_stat_cpu __percpu *stat_cpu;
:  	atomic_long_t		stat[MEMCG_NR_STAT];
:  	atomic_long_t		events[NR_VM_EVENT_ITEMS];
: +	atomic_long_t memory_events[MEMCG_NR_MEMORY_EVENTS];
:
:  	unsigned long		socket_pressure;

And performance restored.

Later investigation found that as long as the following 3 fields
moving_account, move_lock_task and stat_cpu are in the same cacheline,
performance will be good.  To avoid future performance surprise by other
commits changing the layout of 'struct mem_cgroup', this patch makes
sure the 3 fields stay in the same cacheline.

One concern of this approach is, moving_account and move_lock_task could
be modified when a process changes memory cgroup while stat_cpu is a
always read field, it might hurt to place them in the same cacheline.  I
assume it is rare for a process to change memory cgroup so this should
be OK.

Link: https://lkml.kernel.org/r/20180528114019.GF9904@yexl-desktop
Link: http://lkml.kernel.org/r/20180601071115.GA27302@intel.comSigned-off-by: NAaron Lu <aaron.lu@intel.com>
Reported-by: Nkernel test robot <xiaolong.ye@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Memory controller implements the memory.low best-effort memory
protection mechanism, which works perfectly in many cases and allows
protecting working sets of important workloads from sudden reclaim.

But its semantics has a significant limitation: it works only as long as
there is a supply of reclaimable memory.  This makes it pretty useless
against any sort of slow memory leaks or memory usage increases.  This
is especially true for swapless systems.  If swap is enabled, memory
soft protection effectively postpones problems, allowing a leaking
application to fill all swap area, which makes no sense.  The only
effective way to guarantee the memory protection in this case is to
invoke the OOM killer.

It's possible to handle this case in userspace by reacting on MEMCG_LOW
events; but there is still a place for a fail-safe in-kernel mechanism
to provide stronger guarantees.

This patch introduces the memory.min interface for cgroup v2 memory
controller.  It works very similarly to memory.low (sharing the same
hierarchical behavior), except that it's not disabled if there is no
more reclaimable memory in the system.

If cgroup is not populated, its memory.min is ignored, because otherwise
even the OOM killer wouldn't be able to reclaim the protected memory,
and the system can stall.

[guro@fb.com: s/low/min/ in docs]
Link: http://lkml.kernel.org/r/20180510130758.GA9129@castle.DHCP.thefacebook.com
Link: http://lkml.kernel.org/r/20180509180734.GA4856@castle.DHCP.thefacebook.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Reviewed-by: NRandy Dunlap <rdunlap@infradead.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.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>

mem_cgroup_cgwb_list is a very simple wrapper and it will never be used
outside of code under CONFIG_CGROUP_WRITEBACK.  so use memcg->cgwb_list
directly.

Link: http://lkml.kernel.org/r/1524406173-212182-1-git-send-email-wanglong19@meituan.comSigned-off-by: NWang Long <wanglong19@meituan.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch aims to address an issue in current memory.low semantics,
which makes it hard to use it in a hierarchy, where some leaf memory
cgroups are more valuable than others.

For example, there are memcgs A, A/B, A/C, A/D and A/E:

  A      A/memory.low = 2G, A/memory.current = 6G
 //\\
BC  DE   B/memory.low = 3G  B/memory.current = 2G
         C/memory.low = 1G  C/memory.current = 2G
         D/memory.low = 0   D/memory.current = 2G
	 E/memory.low = 10G E/memory.current = 0

If we apply memory pressure, B, C and D are reclaimed at the same pace
while A's usage exceeds 2G.  This is obviously wrong, as B's usage is
fully below B's memory.low, and C has 1G of protection as well.  Also, A
is pushed to the size, which is less than A's 2G memory.low, which is
also wrong.

A simple bash script (provided below) can be used to reproduce
the problem. Current results are:
  A:    1430097920
  A/B:  711929856
  A/C:  717426688
  A/D:  741376
  A/E:  0

To address the issue a concept of effective memory.low is introduced.
Effective memory.low is always equal or less than original memory.low.
In a case, when there is no memory.low overcommittment (and also for
top-level cgroups), these two values are equal.

Otherwise it's a part of parent's effective memory.low, calculated as a
cgroup's memory.low usage divided by sum of sibling's memory.low usages
(under memory.low usage I mean the size of actually protected memory:
memory.current if memory.current < memory.low, 0 otherwise).  It's
necessary to track the actual usage, because otherwise an empty cgroup
with memory.low set (A/E in my example) will affect actual memory
distribution, which makes no sense.  To avoid traversing the cgroup tree
twice, page_counters code is reused.

Calculating effective memory.low can be done in the reclaim path, as we
conveniently traversing the cgroup tree from top to bottom and check
memory.low on each level.  So, it's a perfect place to calculate
effective memory low and save it to use it for children cgroups.

This also eliminates a need to traverse the cgroup tree from bottom to
top each time to check if parent's guarantee is not exceeded.

Setting/resetting effective memory.low is intentionally racy, but it's
fine and shouldn't lead to any significant differences in actual memory
distribution.

With this patch applied results are matching the expectations:
  A:    2147930112
  A/B:  1428721664
  A/C:  718393344
  A/D:  815104
  A/E:  0

Test script:
  #!/bin/bash

  CGPATH="/sys/fs/cgroup"

  truncate /file1 --size 2G
  truncate /file2 --size 2G
  truncate /file3 --size 2G
  truncate /file4 --size 50G

  mkdir "${CGPATH}/A"
  echo "+memory" > "${CGPATH}/A/cgroup.subtree_control"
  mkdir "${CGPATH}/A/B" "${CGPATH}/A/C" "${CGPATH}/A/D" "${CGPATH}/A/E"

  echo 2G > "${CGPATH}/A/memory.low"
  echo 3G > "${CGPATH}/A/B/memory.low"
  echo 1G > "${CGPATH}/A/C/memory.low"
  echo 0 > "${CGPATH}/A/D/memory.low"
  echo 10G > "${CGPATH}/A/E/memory.low"

  echo $$ > "${CGPATH}/A/B/cgroup.procs" && vmtouch -qt /file1
  echo $$ > "${CGPATH}/A/C/cgroup.procs" && vmtouch -qt /file2
  echo $$ > "${CGPATH}/A/D/cgroup.procs" && vmtouch -qt /file3
  echo $$ > "${CGPATH}/cgroup.procs" && vmtouch -qt /file4

  echo "A:   " `cat "${CGPATH}/A/memory.current"`
  echo "A/B: " `cat "${CGPATH}/A/B/memory.current"`
  echo "A/C: " `cat "${CGPATH}/A/C/memory.current"`
  echo "A/D: " `cat "${CGPATH}/A/D/memory.current"`
  echo "A/E: " `cat "${CGPATH}/A/E/memory.current"`

  rmdir "${CGPATH}/A/B" "${CGPATH}/A/C" "${CGPATH}/A/D" "${CGPATH}/A/E"
  rmdir "${CGPATH}/A"
  rm /file1 /file2 /file3 /file4

Link: http://lkml.kernel.org/r/20180405185921.4942-2-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.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>

This patch renames struct page_counter fields:
  count -> usage
  limit -> max

and the corresponding functions:
  page_counter_limit() -> page_counter_set_max()
  mem_cgroup_get_limit() -> mem_cgroup_get_max()
  mem_cgroup_resize_limit() -> mem_cgroup_resize_max()
  memcg_update_kmem_limit() -> memcg_update_kmem_max()
  memcg_update_tcp_limit() -> memcg_update_tcp_max()

The idea behind this renaming is to have the direct matching
between memory cgroup knobs (low, high, max) and page_counters API.

This is pure renaming, this patch doesn't bring any functional change.

Link: http://lkml.kernel.org/r/20180405185921.4942-1-guro@fb.comSigned-off-by: NRoman Gushchin <guro@fb.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.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>

Add swap max and fail events so that userland can monitor and respond to
running out of swap.

I'm not too sure about the fail event.  Right now, it's a bit confusing
which stats / events are recursive and which aren't and also which ones
reflect events which originate from a given cgroup and which targets the
cgroup.  No idea what the right long term solution is and it could just
be that growing them organically is actually the only right thing to do.

Link: http://lkml.kernel.org/r/20180416231151.GI1911913@devbig577.frc2.facebook.comSigned-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit a983b5eb ("mm: memcontrol: fix excessive complexity in
memory.stat reporting") added per-cpu drift to all memory cgroup stats
and events shown in memory.stat and memory.events.

For memory.stat this is acceptable.  But memory.events issues file
notifications, and somebody polling the file for changes will be
confused when the counters in it are unchanged after a wakeup.

Luckily, the events in memory.events - MEMCG_LOW, MEMCG_HIGH, MEMCG_MAX,
MEMCG_OOM - are sufficiently rare and high-level that we don't need
per-cpu buffering for them: MEMCG_HIGH and MEMCG_MAX would be the most
frequent, but they're counting invocations of reclaim, which is a
complex operation that touches many shared cachelines.

This splits memory.events from the generic VM events and tracks them in
their own, unbuffered atomic counters.  That's also cleaner, as it
eliminates the ugly enum nesting of VM and cgroup events.

[hannes@cmpxchg.org: "array subscript is above array bounds"]
  Link: http://lkml.kernel.org/r/20180406155441.GA20806@cmpxchg.org
Link: http://lkml.kernel.org/r/20180405175507.GA24817@cmpxchg.org
Fixes: a983b5eb ("mm: memcontrol: fix excessive complexity in memory.stat reporting")
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NTejun Heo <tj@kernel.org>
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

memcg reclaim may alter pgdat->flags based on the state of LRU lists in
cgroup and its children.  PGDAT_WRITEBACK may force kswapd to sleep
congested_wait(), PGDAT_DIRTY may force kswapd to writeback filesystem
pages.  But the worst here is PGDAT_CONGESTED, since it may force all
direct reclaims to stall in wait_iff_congested().  Note that only kswapd
have powers to clear any of these bits.  This might just never happen if
cgroup limits configured that way.  So all direct reclaims will stall as
long as we have some congested bdi in the system.

Leave all pgdat->flags manipulations to kswapd.  kswapd scans the whole
pgdat, only kswapd can clear pgdat->flags once node is balanced, thus
it's reasonable to leave all decisions about node state to kswapd.

Why only kswapd? Why not allow to global direct reclaim change these
flags? It is because currently only kswapd can clear these flags.  I'm
less worried about the case when PGDAT_CONGESTED falsely not set, and
more worried about the case when it falsely set.  If direct reclaimer
sets PGDAT_CONGESTED, do we have guarantee that after the congestion
problem is sorted out, kswapd will be woken up and clear the flag? It
seems like there is no such guarantee.  E.g.  direct reclaimers may
eventually balance pgdat and kswapd simply won't wake up (see
wakeup_kswapd()).

Moving pgdat->flags manipulation to kswapd, means that cgroup2 recalim
now loses its congestion throttling mechanism.  Add per-cgroup
congestion state and throttle cgroup2 reclaimers if memcg is in
congestion state.

Currently there is no need in per-cgroup PGDAT_WRITEBACK and PGDAT_DIRTY
bits since they alter only kswapd behavior.

The problem could be easily demonstrated by creating heavy congestion in
one cgroup:

    echo "+memory" > /sys/fs/cgroup/cgroup.subtree_control
    mkdir -p /sys/fs/cgroup/congester
    echo 512M > /sys/fs/cgroup/congester/memory.max
    echo $$ > /sys/fs/cgroup/congester/cgroup.procs
    /* generate a lot of diry data on slow HDD */
    while true; do dd if=/dev/zero of=/mnt/sdb/zeroes bs=1M count=1024; done &
    ....
    while true; do dd if=/dev/zero of=/mnt/sdb/zeroes bs=1M count=1024; done &

and some job in another cgroup:

    mkdir /sys/fs/cgroup/victim
    echo 128M > /sys/fs/cgroup/victim/memory.max

    # time cat /dev/sda > /dev/null
    real    10m15.054s
    user    0m0.487s
    sys     1m8.505s

According to the tracepoint in wait_iff_congested(), the 'cat' spent 50%
of the time sleeping there.

With the patch, cat don't waste time anymore:

    # time cat /dev/sda > /dev/null
    real    5m32.911s
    user    0m0.411s
    sys     0m56.664s

[aryabinin@virtuozzo.com: congestion state should be per-node]
  Link: http://lkml.kernel.org/r/20180406135215.10057-1-aryabinin@virtuozzo.com
[ayabinin@virtuozzo.com: make congestion state per-cgroup-per-node instead of just per-cgroup[
  Link: http://lkml.kernel.org/r/20180406180254.8970-2-aryabinin@virtuozzo.com
Link: http://lkml.kernel.org/r/20180323152029.11084-5-aryabinin@virtuozzo.comSigned-off-by: NAndrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

After commit a983b5eb ("mm: memcontrol: fix excessive complexity in
memory.stat reporting"), we observed slowly upward creeping NR_WRITEBACK
counts over the course of several days, both the per-memcg stats as well
as the system counter in e.g.  /proc/meminfo.

The conversion from full per-cpu stat counts to per-cpu cached atomic
stat counts introduced an irq-unsafe RMW operation into the updates.

Most stat updates come from process context, but one notable exception
is the NR_WRITEBACK counter.  While writebacks are issued from process
context, they are retired from (soft)irq context.

When writeback completions interrupt the RMW counter updates of new
writebacks being issued, the decs from the completions are lost.

Since the global updates are routed through the joint lruvec API, both
the memcg counters as well as the system counters are affected.

This patch makes the joint stat and event API irq safe.

Link: http://lkml.kernel.org/r/20180203082353.17284-1-hannes@cmpxchg.org
Fixes: a983b5eb ("mm: memcontrol: fix excessive complexity in memory.stat reporting")
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Debugged-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NRik van Riel <riel@surriel.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>