linux-kernel - Re: OOM Killer don't works at all if the system have >gigabytes memory (was Re: [PATCH] mm: check zone->all_unreclaimable in all

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Date:	Tue, 10 May 2011 22:30:44 -0400 (EDT)
From:	CAI Qian <caiqian@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	avagin@...il.com, Andrey Vagin <avagin@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Minchan Kim <minchan.kim@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: OOM Killer don't works at all if the system have >gigabytes
 memory (was Re: [PATCH] mm: check zone->all_unreclaimable in
 all_unreclaimable())



----- Original Message -----
> (cc to oom interested people)
> 
> > > > > I have tested this for the latest mainline kernel using the
> > > > > reproducer
> > > > > attached, the system just hung or deadlock after oom. The
> > > > > whole oom
> > > > > trace is here.
> > > > > http://people.redhat.com/qcai/oom.log
> > > > >
> > > > > Did I miss anything?
> > > >
> > > > Can you please try commit
> > > > 929bea7c714220fc76ce3f75bef9056477c28e74?
> > > As I have mentioned that I have tested the latest mainline which
> > > have
> > > already included that fix. Also, does this problem only for x86?
> > > The
> > > testing was done using x86_64. Not sure if that would be a
> > > problem.
> >
> > No. I'm also using x86_64 and my machine completely works on current
> > latest linus tree. I confirmed it today.
> 
> > 4194288 pages RAM
> 
> You have 16GB RAM.
> 
> > Out of memory: Kill process 1175 (dhclient) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1247 (rsyslogd) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1284 (irqbalance) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1303 (rpcbind) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1321 (rpc.statd) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1333 (mdadm) score 1 or sacrifice child
> > Out of memory: Kill process 1365 (rpc.idmapd) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1403 (dbus-daemon) score 1 or sacrifice
> > child
> > Out of memory: Kill process 1438 (acpid) score 1 or sacrifice child
> > Out of memory: Kill process 1447 (hald) score 1 or sacrifice child
> > Out of memory: Kill process 1447 (hald) score 1 or sacrifice child
> > Out of memory: Kill process 1487 (hald-addon-inpu) score 1 or
> > sacrifice child
> > Out of memory: Kill process 1488 (hald-addon-acpi) score 1 or
> > sacrifice child
> > Out of memory: Kill process 1507 (automount) score 1 or sacrifice
> > child
> 
> Oops.
> 
> OK. That's known issue. Current OOM logic doesn't works if you have
> gigabytes RAM. because _all_ process have the exactly same score (=1).
> then oom killer just fallback to random process killer. It was made
> commit a63d83f427 (oom: badness heuristic rewrite). I pointed out
> it at least three times. You have to blame Google folks. :-/
> 
> 
> The problems are three.
> 
> 1) if two processes have the same oom score, we should kill younger
> process.
> but current logic kill older. Oldest processes are typicall system
> daemons.
> 2) Current logic use 'unsigned int' for internal score calculation.
> (exactly says,
> it only use 0-1000 value). its very low precision calculation makes a
> lot of
> same oom score and kill an ineligible process.
> 3) Current logic give 3% of SystemRAM to root processes. It obviously
> too big
> if you have plenty memory. Now, your fork-bomb processes have 500MB
> OOM immune
> bonus. then your fork-bomb never ever be killed.
> 
> 
> CAI-san: I've made fixing patches. Can you please try them?
Sure, I saw there were some discussion going on between you and David
about your patches. Does it make more sense for me to test those after
you have settled down technical arguments?
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