linux-kernel - Re: Memory overcommit

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Date:	Wed, 4 Nov 2009 12:19:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	vedran.furac@...il.com, Hugh Dickins <hugh.dickins@...cali.co.uk>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	minchan.kim@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: Memory overcommit

On Tue, 3 Nov 2009 19:10:34 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 4 Nov 2009, KAMEZAWA Hiroyuki wrote:
> 
> > My point and your point are differnt.
> > 
> >   1. All my concern is "baseline for heuristics"
> >   2. All your concern is "baseline for knob, as oom_adj"
> > 
> > ok ? For selecting victim by the kernel, dynamic value is much more useful.
> > Current behavior of "Random kill" and "Kill multiple processes" are too bad.
> > Considering oom-killer is for what, I think "1" is more important.
> > 
> > But I know what you want, so, I offers new knob which is not affected by RSS
> > as I wrote in previous mail.
> > 
> > Off-topic:
> > As memcg is growing better, using OOM-Killer for resource control should be
> > ended, I think. Maybe Fake-NUMA+cpuset is working well for google system, 
> > but plz consider to use memcg. 
> > 
> 
> I understand what you're trying to do, and I agree with it for most 
> desktop systems.  However, I think that admins should have a very strong 
> influence in what tasks the oom killer kills.  It doesn't really matter if 
> it's via oom_adj or not, and its debatable whether an adjustment on a 
> static heuristic score is in our best interest in the first place.  But we 
> must have an alternative so that our control over oom killing isn't lost.
> 
I'll not go too quickly, so, let's discuss and rewrite patches more, later.
I'll parepare new version in the next week. For this week, I'll post
swap accounting and improve fork-bomb detector.

> I'd also like to open another topic for discussion if you're proposing 
> such sweeping changes: at what point do we allow ~__GFP_NOFAIL allocations 
> to fail even if order < PAGE_ALLOC_COSTLY_ORDER and defer killing 
> anything?  We both agreed that it's not always in the best interest to 
> kill a task so that an allocation can succeed, so we need to define some 
> criteria to simply fail the allocation instead.
> 
Yes, I think allocation itself (> order=0) should fail more before we finally
invoke OOM. It tends to be soft-landing rather than oom-killer.

Thanks,
-Kame

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