+ memcg-oom-check-memcg-margin-for-parallel-oom.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: memcg, oom: check memcg margin for parallel oom
has been added to the -mm tree.  Its filename is
     memcg-oom-check-memcg-margin-for-parallel-oom.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/memcg-oom-check-memcg-margin-for-parallel-oom.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/memcg-oom-check-memcg-margin-for-parallel-oom.patch

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------------------------------------------------------
From: Yafang Shao <laoar.shao@gmail.com>
Subject: memcg, oom: check memcg margin for parallel oom

Memcg oom killer invocation is synchronized by the global oom_lock and
tasks are sleeping on the lock while somebody is selecting the victim or
potentially race with the oom_reaper is releasing the victim's memory. 
This can result in a pointless oom killer invocation because a waiter
might be racing with the oom_reaper

        P1              oom_reaper              P2
                        oom_reap_task           mutex_lock(oom_lock)
                                                out_of_memory # no victim because we have one already
                        __oom_reap_task_mm      mute_unlock(oom_lock)
 mutex_lock(oom_lock)
                        set MMF_OOM_SKIP
 select_bad_process
 # finds a new victim

The page allocator prevents from this race by trying to allocate after the
lock can be acquired (in __alloc_pages_may_oom) which acts as a last
minute check.  Moreover page allocator simply doesn't block on the
oom_lock and simply retries the whole reclaim process.

Memcg oom killer should do the last minute check as well.  Call
mem_cgroup_margin to do that.  Trylock on the oom_lock could be done as
well but this doesn't seem to be necessary at this stage.

[mhocko@kernel.org: commit log]
Link: http://lkml.kernel.org/r/1594735034-19190-1-git-send-email-laoar.shao@gmail.com
Suggested-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c~memcg-oom-check-memcg-margin-for-parallel-oom
+++ a/mm/memcontrol.c
@@ -1665,15 +1665,21 @@ static bool mem_cgroup_out_of_memory(str
 		.gfp_mask = gfp_mask,
 		.order = order,
 	};
-	bool ret;
+	bool ret = true;
 
 	if (mutex_lock_killable(&oom_lock))
 		return true;
+
+	if (mem_cgroup_margin(memcg) >= (1 << order))
+		goto unlock;
+
 	/*
 	 * A few threads which were not waiting at mutex_lock_killable() can
 	 * fail to bail out. Therefore, check again after holding oom_lock.
 	 */
 	ret = should_force_charge() || out_of_memory(&oc);
+
+unlock:
 	mutex_unlock(&oom_lock);
 	return ret;
 }
_

Patches currently in -mm which might be from laoar.shao@gmail.com are

mm-memcg-avoid-stale-protection-values-when-cgroup-is-above-protection.patch
memcg-oom-check-memcg-margin-for-parallel-oom.patch
mm-oom-make-the-calculation-of-oom-badness-more-accurate.patch
mm-oom-make-the-calculation-of-oom-badness-more-accurate-v3.patch