linux-kernel - Re: [RFC] oom-kill: give the dying task a higher priority

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Date:	Tue, 1 Jun 2010 11:36:05 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Peter Zijlstra <peterz@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	balbir@...ux.vnet.ibm.com, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Mel Gorman <mel@....ul.ie>, williams@...hat.com
Subject: Re: [RFC] oom-kill: give the dying task a higher priority

On Tue, 1 Jun 2010, Minchan Kim wrote:

> Secondly, as Kame pointed out, we have to raise whole thread's
> priority to kill victim process for reclaiming pages. But I think it
> has deadlock problem.

Agreed, this has the potential to actually increase the amount of time for 
an oom killed task to fully exit: the exit path takes mm->mmap_sem on exit 
and if that is held by another thread waiting for the oom killed task to 
exit (i.e. reclaim has failed and the oom killer becomes a no-op because 
it sees an already killed task) then there's a livelock.  That's always 
been a problem, but is compounded with increasing the priority of a task 
not holding mm->mmap_sem if the thread holding the writelock actually 
isn't looking for memory but simply doesn't get a chance to release 
because it fails to run.
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