From: Frans Pop <elendil@planet.nl>
To: Mel Gorman <mel@csn.ul.ie>
Subject: Re: [Bug #14141] order 2 page allocation failures in iwlagn
Date: Fri, 6 Nov 2009 10:51:37 +0100
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Cc: Chris Mason <chris.mason@oracle.com>, David Rientjes <rientjes@google.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Kernel Testers List <kernel-testers@vger.kernel.org>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       Reinette Chatre <reinette.chatre@intel.com>,
       Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>,
       Karol Lewandowski <karol.k.lewandowski@gmail.com>,
       Mohamed Abbas <mohamed.abbas@intel.com>,
       Jens Axboe <jens.axboe@oracle.com>,
       "John W. Linville" <linville@tuxdriver.com>, linux-mm@kvack.org
References: <3onW63eFtRF.A.xXH.oMTxKB@chimera> <200910262206.13146.elendil@planet.nl> <200911052114.36718.elendil@planet.nl>
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On Thursday 05 November 2009, Frans Pop wrote:
> On Monday 26 October 2009, Frans Pop wrote:
> > On Tuesday 20 October 2009, Mel Gorman wrote:
> > > I've attached a patch below that should allow us to cheat. When it's
> > > applied, it outputs who called congestion_wait(), how long the
> > > timeout was and how long it waited for. By comparing before and
> > > after sleep times, we should be able to see which of the callers has
> > > significantly changed and if it's something easily addressable.
> >
> > The results from this look fairly interesting (although I may be a bad
> > judge as I don't really know what I'm looking at ;-).
> >
> > I've tested with two kernels:
> > 1) 2.6.31.1: 1 test run
> > 2) 2.6.31.1 + congestion_wait() reverts: 2 test runs
>
> I've taken another look at the data from this debug patch, resulting in
> these graphs: http://people.debian.org/~fjp/tmp/kernel/congestion.pdf
>
> I think the graph may show the reason for the congestion_wait()
> regression. Horizontal axis shows time, vertical axis shows number of
> logged congestion_wait calls per type.

I'm sorry. My initial version had a skewed time axis (showed occurrences 
instead of actual time). I've now uploaded a corrected version:
http://people.debian.org/~fjp/tmp/kernel/congestion.pdf

I've also uploaded a second version that shows cumulative delay per type, 
which probably gives a better insight:
http://people.debian.org/~fjp/tmp/kernel/congestion2.pdf

For both the top chart is without the revert, the bottom one after the 
revert.
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