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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [patch -mm 13/18] oom: avoid race for oom killed tasks detaching mm prior to exit
In-Reply-To: <alpine.DEB.2.00.1006010016460.29202@chino.kir.corp.google.com>
References: <alpine.DEB.2.00.1006010008410.29202@chino.kir.corp.google.com> <alpine.DEB.2.00.1006010016460.29202@chino.kir.corp.google.com>
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Date: Tue,  1 Jun 2010 16:40:43 +0900 (JST)
Sender: owner-linux-mm@kvack.org
To: David Rientjes <rientjes@google.com>
Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Nick Piggin <npiggin@suse.de>, Oleg Nesterov <oleg@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>

> Tasks detach its ->mm prior to exiting so it's possible that in progress
> oom kills or already exiting tasks may be missed during the oom killer's
> tasklist scan.  When an eligible task is found with either TIF_MEMDIE or
> PF_EXITING set, the oom killer is supposed to be a no-op to avoid
> needlessly killing additional tasks.  This closes the race between a task
> detaching its ->mm and being removed from the tasklist.
> 
> Out of memory conditions as the result of memory controllers will
> automatically filter tasks that have detached their ->mm (since
> task_in_mem_cgroup() will return 0).  This is acceptable, however, since
> memcg constrained ooms aren't the result of a lack of memory resources but
> rather a limit imposed by userspace that requires a task be killed
> regardless.
> 
> [oleg@redhat.com: fix PF_EXITING check for !p->mm tasks]
> Acked-by: Nick Piggin <npiggin@suse.de>
> Signed-off-by: David Rientjes <rientjes@google.com>

need respin.


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