linux-kernel - Re: [PATCH 0/5] Reduce GFP_ATOMIC allocation failures, candidate fix V3

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Date:	Mon, 16 Nov 2009 17:57:39 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Frans Pop <elendil@...net.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stephan von Krawczynski <skraw@...net.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: [PATCH 0/5] Reduce GFP_ATOMIC allocation failures, candidate
	fix V3

On Fri, Nov 13, 2009 at 10:04:21AM +0100, Frans Pop wrote:
> On Thursday 12 November 2009, Mel Gorman wrote:
> > Changelog since V2
> >   o Dropped the kswapd-quickly-notice-high-order patch. In more detailed
> >     testing, it made latencies even worse as kswapd slept more on
> >     high-order congestion causing order-0 direct reclaims.
> >   o Added changes to how congestion_wait() works
> >   o Added a number of new patches altering the behaviour of reclaim
> 
> I have tested this series on top of .32-rc7. First impression is that it 
> does seem to improve my test case, but does not yet completely solve it.
> 
> My last gitk instance now loads more smoothly for most of the time it takes 
> to complete, but I still see a choke point where things freeze for a while 
> and where I get SKB allocation errors from my wireless.
> However, that choke point does seem to happen later and to be shorter than 
> without the patches.
> 

I haven't fully figured out why this makes a difference yet, but with
.32-rc7 and these patches, could you retry the test except beforehand do

cd /sys
for SYS in `find -name low_latency`; do
        echo 0 > $SYS
done

I believe the low_latency logic might be interfering with the number of
clean pages available for kswapd to reclaim.

Thanks

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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