linux-kernel - Re: [PATCH 3/5] oom: create oom autogroup

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Message-ID: <1300848099.7492.14.camel@marge.simson.net>
Date:	Wed, 23 Mar 2011 03:41:39 +0100
From:	Mike Galbraith <efault@....de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Subject: Re: [PATCH 3/5] oom: create oom autogroup

On Wed, 2011-03-23 at 10:27 +0900, KOSAKI Motohiro wrote:
> > On Tue, Mar 22, 2011 at 8:08 PM, KOSAKI Motohiro
> > <kosaki.motohiro@...fujitsu.com> wrote:
> > > When plenty processes (eg fork bomb) are running, the TIF_MEMDIE task
> > > never exit, at least, human feel it's never. therefore kernel become
> > > hang-up.
> > >
> > > "perf sched" tell us a hint.
> > >
> > >  ------------------------------------------------------------------------------
> > >  Task                  |   Runtime ms  | Average delay ms | Maximum delay ms |
> > >  ------------------------------------------------------------------------------
> > >  python:1754           |      0.197 ms | avg: 1731.727 ms | max: 3433.805 ms |
> > >  python:1843           |      0.489 ms | avg: 1707.433 ms | max: 3622.955 ms |
> > >  python:1715           |      0.220 ms | avg: 1707.125 ms | max: 3623.246 ms |
> > >  python:1818           |      2.127 ms | avg: 1527.331 ms | max: 3622.553 ms |
> > >  ...
> > >  ...
> > >
> > > Processes flood makes crazy scheduler delay. and then the victim process
> > > can't run enough. Grr. Should we do?
> > >
> > > Fortunately, we already have anti process flood framework, autogroup!
> > > This patch reuse this framework and avoid kernel live lock.
> > 
> > That's cool idea but I have a concern.
> > 
> > You remove boosting priority in [2/5] and move victim tasks into autogroup.
> > If I understand autogroup right, victim process and threads in the
> > process take less schedule chance than now.
> 
> Right. Icky cpu-cgroup rt-runtime default enforce me to seek another solution.

I was going to mention rt, and there's s/fork/clone as well.

> Today, I got private mail from Luis and he seems to have another improvement
> idea. so, I might drop this patch if his one works fine.

Perhaps if TIF_MEMDIE threads needs special treatment, preemption tests
could take that into account?  (though I don't like touching fast path
for oddball cases)

	-Mike





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