linux-kernel - Re: [PATCH 0/5] Candidate fix for increased number of GFP

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Date:	Thu, 22 Oct 2009 17:03:10 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	David Miller <davem@...emloft.net>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Kalle Valo <kalle.valo@....fi>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mohamed Abbas <mohamed.abbas@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"John W. Linville" <linville@...driver.com>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Stephan von Krawczynski <skraw@...net.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	akpm@...ux-foundation.org, cl@...ux-foundation.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 0/5] Candidate fix for increased number of GFP_ATOMIC
	failures V2

On Thu, Oct 22, 2009 at 05:47:10PM +0300, Pekka Enberg wrote:
> On Thu, Oct 22, 2009 at 5:22 PM, Mel Gorman <mel@....ul.ie> wrote:
> > Test 1: Verify your problem occurs on 2.6.32-rc5 if you can
> >
> > Test 2: Apply the following two patches and test again
> >
> >  1/5 page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed
> >  2/5 page allocator: Do not allow interrupts to use ALLOC_HARDER
> 
> These are pretty obvious bug fixes and should go to linux-next ASAP IMHO.
> 

Agreed, but I wanted to pin down where exactly we stand with this
problem before sending patches any direction for merging.

> > Test 5: If things are still screwed, apply the following
> >  5/5 Revert 373c0a7e, 8aa7e847: Fix congestion_wait() sync/async vs read/write confusion
> >
> >        Frans Pop reports that the bulk of his problems go away when this
> >        patch is reverted on 2.6.31. There has been some confusion on why
> >        exactly this patch was wrong but apparently the conversion was not
> >        complete and further work was required. It's unknown if all the
> >        necessary work exists in 2.6.31-rc5 or not. If there are still
> >        allocation failures and applying this patch fixes the problem,
> >        there are still snags that need to be ironed out.
> 
> As explained by Jens Axboe, this changes timing but is not the source
> of the OOMs so the revert is bogus even if it "helps" on some
> workloads. IIRC the person who reported the revert to help things did
> report that the OOMs did not go away, they were simply harder to
> trigger with the revert.
> 

IIRC, there were mixed reports as to how much the revert helped.  I'm hoping
that patches 1+2 cover the bases hence why I asked them to be tested on
their own. Patch 2 in particular might be responsible for watermarks being
impacted enough to cause timing problems. I left reverting with patch 5 as
a standalone test to see how much of a factor the timing changes introduced
are if there are still allocation problems.

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