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From: Michal Hocko <mhocko@suse.cz>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Balbir Singh <bsingharora@gmail.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	cgroups@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch v2] oom, memcg: fix exclusion of memcg threads after they have detached their mm
Date: Thu, 15 Dec 2011 16:59:26 +0100	[thread overview]
Message-ID: <20111215155926.GA22819@tiehlicka.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.00.1112141838470.27595@chino.kir.corp.google.com>

On Wed 14-12-11 18:39:40, David Rientjes wrote:
> oom, memcg: fix exclusion of memcg threads after they have detached their mm
> 
> The oom killer relies on logic that identifies threads that have already
> been oom killed when scanning the tasklist and, if found, deferring until
> such threads have exited.  This is done by checking for any candidate
> threads that have the TIF_MEMDIE bit set.
> 
> For memcg ooms, candidate threads are first found by calling
> task_in_mem_cgroup() since the oom killer should not defer if there's an
> oom killed thread in another memcg.
> 
> Unfortunately, task_in_mem_cgroup() excludes threads if they have
> detached their mm in the process of exiting so TIF_MEMDIE is never
> detected for such conditions.  This is different for global, mempolicy,
> and cpuset oom conditions where a detached mm is only excluded after
> checking for TIF_MEMDIE and deferring, if necessary, in
> select_bad_process().
> 
> The fix is to return true if a task has a detached mm but is still in the
> memcg or its hierarchy that is currently oom.  This will allow the oom
> killer to appropriately defer rather than kill unnecessarily or, in the
> worst case, panic the machine if nothing else is available to kill.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/memcontrol.c |   17 +++++++++++++----
>  1 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1109,10 +1109,19 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
>  	struct task_struct *p;
>  
>  	p = find_lock_task_mm(task);
> -	if (!p)
> -		return 0;
> -	curr = try_get_mem_cgroup_from_mm(p->mm);
> -	task_unlock(p);
> +	if (p) {
> +		curr = try_get_mem_cgroup_from_mm(p->mm);
> +		task_unlock(p);
> +	} else {
> +		/*
> +		 * All threads may have already detached their mm's, but the oom
> +		 * killer still needs to detect if they have already been oom
> +		 * killed to prevent needlessly killing additional tasks.
> +		 */
> +		curr = mem_cgroup_from_task(task);
> +		if (curr)
> +			css_get(&curr->css);

Sorry, but I forgot to mention that we need task_lock(task) around
css_get.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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  parent reply	other threads:[~2011-12-15 15:59 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-14  0:59 [patch] oom, memcg: fix exclusion of memcg threads after they have detached their mm David Rientjes
2011-12-14  1:06 ` KAMEZAWA Hiroyuki
2011-12-14 10:29 ` Michal Hocko
2011-12-15  2:39   ` [patch v2] " David Rientjes
2011-12-15 14:19     ` KOSAKI Motohiro
2011-12-15 15:59     ` Michal Hocko [this message]
2011-12-15 21:36       ` [patch v3] " David Rientjes
2011-12-15 22:18         ` KAMEZAWA Hiroyuki
2011-12-16  8:31         ` Michal Hocko

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