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

Commit Message

Andrew Morton Aug. 7, 2020, 6:22 a.m. UTC

From: Yafang Shao <[e-mail]>
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.

[[e-mail]: commit log]
Link: http://lkml.kernel.org/r/[e-mail]
Suggested-by: Michal Hocko <[e-mail]>
Signed-off-by: Yafang Shao <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: Chris Down <[e-mail]>
Cc: Tetsuo Handa <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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;
 }