linux-kernel - Re: [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks

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Date:   Tue, 6 Nov 2018 13:42:24 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] memcg: do not report racy no-eligible OOM tasks

On Tue 06-11-18 18:44:43, Tetsuo Handa wrote:
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6e1469b..a97648a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1382,8 +1382,13 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	};
>  	bool ret;
>  
> -	mutex_lock(&oom_lock);
> -	ret = out_of_memory(&oc);
> +	if (mutex_lock_killable(&oom_lock))
> +		return true;
> +	/*
> +	 * A few threads which were not waiting at mutex_lock_killable() can
> +	 * fail to bail out. Therefore, check again after holding oom_lock.
> +	 */
> +	ret = fatal_signal_pending(current) || out_of_memory(&oc);
>  	mutex_unlock(&oom_lock);
>  	return ret;
>  }

If we are goging with a memcg specific thingy then I really prefer
tsk_is_oom_victim approach. Or is there any reason why this is not
suitable?

-- 
Michal Hocko
SUSE Labs