memcg, oom: check memcg margin for parallel oom

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]

Suggested-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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>
Link: http://lkml.kernel.org/r/1594735034-19190-1-git-send-email-laoar.shao@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>