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Date: Mon, 3 Jun 2013 18:31:34 +0200
From: Michal Hocko <mhocko@suse.cz>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        cgroups@vger.kernel.org
Subject: Re: [patch] mm, memcg: add oom killer delay
Message-ID: <20130603163012.GA23257@dhcp22.suse.cz>
References: <alpine.DEB.2.02.1305291817280.520@chino.kir.corp.google.com>
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On Sat 01-06-13 02:11:51, Johannes Weiner wrote:
> @@ -2076,6 +2077,7 @@ static void memcg_wakeup_oom(struct mem_cgroup *memcg)
>  {
>  	/* for filtering, pass "memcg" as argument. */
>  	__wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
> +	atomic_inc(&memcg->oom_wakeups);
>  }
>  
>  static void memcg_oom_recover(struct mem_cgroup *memcg)
[...]
> +	prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
> +	/* Only sleep if we didn't miss any wakeups since OOM */
> +	if (atomic_read(&memcg->oom_wakeups) == current->memcg_oom.wakeups)
> +		schedule();

On the way home it occured to me that the ordering might be wrong here.
The wake up can be lost here.
					__wake_up(memcg_oom_waitq)
					<preempted>
prepare_to_wait
atomic_read(&memcg->oom_wakeups)
					atomic_inc(oom_wakeups)

I guess we want atomic_inc before __wake_up, right?
-- 
Michal Hocko
SUSE Labs
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