linux-kernel - Re: Found the commit that causes the OOMs

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Message-Id: <20090705193551.090E.A69D9226@jp.fujitsu.com>
Date:	Sun,  5 Jul 2009 19:38:54 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	David Howells <dhowells@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"Barnes, Jesse" <jesse.barnes@...el.com>
Subject: Re: Found the commit that causes the OOMs

> >> OK. thanks.
> >> I plan to submit this patch after small more tests. it is useful for OOM analysis.
> >
> > It is also useful for throttling page reclaim.
> >
> > If more than half of the inactive pages in a zone are
> > isolated, we are probably beyond the point where adding
> > additional reclaim processes will do more harm than good.
> 
> Maybe we can try limiting the isolation phase of direct reclaims to
> one per CPU?
> 
>         mutex_lock(per_cpu_lock);
>         isolate_pages();
>         shrink_page_list();
>         put_back_pages();
>         mutex_unlock(per_cpu_lock);
> 
> This way the isolated pages as well as major parts of direct reclaims
> will be bounded by CPU numbers. The added overheads should be trivial
> comparing to the reclaim costs.

hm, this idea makes performance degression on few CPU machine, I think.

e.g.
if system have only one cpu and sysmtem makes lumpy reclaim, lumpy reclaim
makes synchronous pageout and it makes very long waiting time.

I suspect per-cpu decision is not useful in this area.

thanks.


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