From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks
Date: Tue, 8 Jan 2019 05:59:49 +0900 [thread overview]
Message-ID: <fa8892d1-4a38-dccd-9597-923924aa0a66@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20190107143802.16847-3-mhocko@kernel.org>
On 2019/01/07 23:38, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> Tetsuo has reported [1] that a single process group memcg might easily
> swamp the log with no-eligible oom victim reports due to race between
> the memcg charge and oom_reaper
This explanation is outdated. I reported that one memcg OOM killer can
kill all processes in that memcg. I expect the changelog to be updated.
>
> Thread 1 Thread2 oom_reaper
> try_charge try_charge
> mem_cgroup_out_of_memory
> mutex_lock(oom_lock)
> mem_cgroup_out_of_memory
> mutex_lock(oom_lock)
> out_of_memory
> select_bad_process
> oom_kill_process(current)
> wake_oom_reaper
> oom_reap_task
> MMF_OOM_SKIP->victim
> mutex_unlock(oom_lock)
> out_of_memory
> select_bad_process # no task
>
> If Thread1 didn't race it would bail out from try_charge and force the
> charge. We can achieve the same by checking tsk_is_oom_victim inside
> the oom_lock and therefore close the race.
>
> [1] http://lkml.kernel.org/r/bb2074c0-34fe-8c2c-1c7d-db71338f1e7f@i-love.sakura.ne.jp
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/memcontrol.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index af7f18b32389..90eb2e2093e7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1387,10 +1387,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> .gfp_mask = gfp_mask,
> .order = order,
> };
> - bool ret;
> + bool ret = true;
>
> mutex_lock(&oom_lock);
And because of "[PATCH 1/2] mm, oom: marks all killed tasks as oom
victims", mark_oom_victim() will be called on current thread even if
we used mutex_lock_killable(&oom_lock) here, like you said
mutex_lock_killable would take care of exiting task already. I would
then still prefer to check for mark_oom_victim because that is not racy
with the exit path clearing signals. I can update my patch to use
_killable lock variant if we are really going with the memcg specific
fix.
. If current thread is not yet killed by the OOM killer but can terminate
without invoking the OOM killer, using mutex_lock_killable(&oom_lock) here
saves some processes. What is the race you are referring by "racy with the
exit path clearing signals" ?
> +
> + /*
> + * multi-threaded tasks might race with oom_reaper and gain
> + * MMF_OOM_SKIP before reaching out_of_memory which can lead
> + * to out_of_memory failure if the task is the last one in
> + * memcg which would be a false possitive failure reported
> + */
Not only out_of_memory() failure. Current thread needlessly tries to
select next OOM victim. out_of_memory() failure is nothing but a result
of no eligible candidate case.
> + if (tsk_is_oom_victim(current))
> + goto unlock;
> +
> ret = out_of_memory(&oc);
> +
> +unlock:
> mutex_unlock(&oom_lock);
> return ret;
> }
>
next prev parent reply other threads:[~2019-01-07 21:00 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-07 14:38 [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM Michal Hocko
2019-01-07 14:38 ` [PATCH 1/2] mm, oom: marks all killed tasks as oom victims Michal Hocko
2019-01-07 20:58 ` Tetsuo Handa
2019-01-08 8:11 ` Michal Hocko
2019-01-07 14:38 ` [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks Michal Hocko
2019-01-07 20:59 ` Tetsuo Handa [this message]
2019-01-08 8:14 ` Michal Hocko
2019-01-08 10:39 ` Tetsuo Handa
2019-01-08 11:46 ` Michal Hocko
2019-01-08 8:35 ` kbuild test robot
2019-01-08 9:39 ` Michal Hocko
2019-01-11 0:23 ` [kbuild-all] " Rong Chen
2019-01-08 14:21 ` [PATCH 3/2] memcg: Facilitate termination of memcg OOM victims Tetsuo Handa
2019-01-08 14:38 ` Michal Hocko
2019-01-09 11:03 ` [PATCH 0/2] oom, memcg: do not report racy no-eligible OOM Michal Hocko
2019-01-09 11:34 ` Tetsuo Handa
2019-01-09 12:02 ` Michal Hocko
2019-01-10 23:59 ` Tetsuo Handa
2019-01-11 10:25 ` Tetsuo Handa
2019-01-11 11:33 ` Michal Hocko
2019-01-11 12:40 ` Tetsuo Handa
2019-01-11 13:34 ` Michal Hocko
2019-01-11 14:31 ` Tetsuo Handa
2019-01-11 15:07 ` Michal Hocko
2019-01-11 15:37 ` Tetsuo Handa
2019-01-11 16:45 ` Michal Hocko
2019-01-12 10:52 ` Tetsuo Handa
2019-01-13 17:36 ` Michal Hocko
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