linux-kernel - Re: [PATCH 0/3] OOM detection rework v4

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Message-ID: <20151218163553.GC4201@cmpxchg.org>
Date:	Fri, 18 Dec 2015 11:35:53 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] OOM detection rework v4

On Fri, Dec 18, 2015 at 02:15:09PM +0100, Michal Hocko wrote:
> On Wed 16-12-15 15:58:44, Andrew Morton wrote:
> > It's hard to say how long declaration of oom should take.  Correctness
> > comes first.  But what is "correct"?  oom isn't a binary condition -
> > there's a chance that if we keep churning away for another 5 minutes
> > we'll be able to satisfy this allocation (but probably not the next
> > one).  There are tradeoffs between promptness-of-declaring-oom and
> > exhaustiveness-in-avoiding-it.
> 
> Yes, this is really hard to tell. What I wanted to achieve here is a
> determinism - the same load should give comparable results. It seems
> that there is an improvement in this regards. The time to settle is 
> much more consistent than with the original implementation.

+1

Before that we couldn't even really make a meaningful statement about
how long we are going to try - "as long as reclaim thinks it can maybe
do some more, depending on heuristics". I think the best thing we can
strive for with OOM is to make the rules simple and predictable.
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