[patch 090/163] memcg, oom: check memcg margin for parallel oom

Andrew Morton
2020-08-07T06:22:12Z

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
@@ -1663,15 +1663,21 @@ 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;
}
_