linux-kernel - Re: [PATCH 1/4] vmscan: all_unreclaimable() use zone->all

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Message-Id: <20110412195513.B533.A69D9226@jp.fujitsu.com>
Date:	Tue, 12 Apr 2011 19:55:14 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Andrey Vagin <avagin@...nvz.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/4] vmscan: all_unreclaimable() use zone->all_unreclaimable as a name

Hi

> > The above says "Eventually, oom-killer never works". Is this no enough?
> > The above says
> >   1) current logic have a race
> >   2) x86 increase a chance of the race by dma zone
> >   3) if race is happen, oom killer don't work
> 
> And the system hangs up, so it's a local DoS and I guess we should
> backport the fix into -stable.  I added this:
> 
> : This resulted in the kernel hanging up when executing a loop of the form
> : 
> : 1. fork
> : 2. mmap
> : 3. touch memory
> : 4. read memory
> : 5. munmmap
> : 
> : as described in
> : http://www.gossamer-threads.com/lists/linux/kernel/1348725#1348725
> 
> And the problems which the other patches in this series address are
> pretty deadly as well.  Should we backport everything?

patch [1/4] and [2/4] should be backported because they are regression fix.
But [3/4] and [4/4] are on borderline to me. they improve a recovery time 
from oom. some times it is very important, some times not. And it is not
regression fix. Our oom-killer is very weak from forkbomb attack since
very old days.

Thanks.


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