linux-kernel - Re: [PATCH] oom: skip frozen tasks

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Message-ID: <20110826070946.GA7280@tiehlicka.suse.cz>
Date:	Fri, 26 Aug 2011 09:09:46 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] oom: skip frozen tasks

On Thu 25-08-11 14:14:20, David Rientjes wrote:
> On Thu, 25 Aug 2011, Michal Hocko wrote:
> 
> > > > > That's obviously false since we call oom_killer_disable() in 
> > > > > freeze_processes() to disable the oom killer from ever being called in the 
> > > > > first place, so this is something you need to resolve with Rafael before 
> > > > > you cause more machines to panic.
> > > >
> > > > I didn't mean suspend/resume path (that is protected by oom_killer_disabled)
> > > > so the patch doesn't make any change.
> > > 
> > > Confused... freeze_processes() does try_to_freeze_tasks() before
> > > oom_killer_disable() ?
> > 
> > Yes you are right, I must have been blind. 
> > 
> > Now I see the point. We do not want to panic while we are suspending and
> > the memory is really low just because all the userspace is already in
> > the the fridge.
> > Sorry for confusion.
> > 
> > I still do not follow the oom_killer_disable note from David, though.
> > 
> 
> oom_killer_disable() was added to that path for a reason when all threads 
> are frozen: memory allocations still occur in the suspend path in an oom 
> condition and adding the oom_killer_disable() will cause those 
> allocations to fail rather than sending pointless SIGKILLs to frozen 
> threads.
> 
> Now consider if the only _eligible_ threads for oom kill (because of 
> cpusets or mempolicies) are those that are frozen.  We certainly do not 
> want to panic because other cpusets are still getting work done.  We'd 
> either want to add a mem to the cpuset or thaw the processes because the 
> cpuset is oom.

Sure.

> 
> You can't just selectively skip certain threads when their state can be 
> temporary without risking a panic.  That's why this patch is a 
> non-starter.
> 
> A much better solution would be to lower the badness score that the oom 
> killer uses for PF_FROZEN threads so that they aren't considered a 
> priority for kill unless there's nothing else left to kill.

Yes, sounds better.

Thanks
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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