From: Mel Gorman Subject: Re: [PATCH 0/3] Reduce impact to overall system of SLUB using high-order allocations Date: Fri, 13 May 2011 12:25:45 +0100 Message-ID: <20110513112545.GG3569@suse.de> References: <1305127773-10570-1-git-send-email-mgorman@suse.de> <1305149960.2606.53.camel@mulgrave.site> <1305153267.2606.57.camel@mulgrave.site> <4DCBC0E8.5020609@cs.helsinki.fi> <1305209096.2575.14.camel@mulgrave.site> <1305215624.2575.52.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Cc: Pekka Enberg , David Rientjes , Andrew Morton , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Christoph Lameter , Rik van Riel , Johannes Weiner , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 To: James Bottomley Return-path: Received: from cantor2.suse.de ([195.135.220.15]:48011 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932213Ab1EMLZt (ORCPT ); Fri, 13 May 2011 07:25:49 -0400 Content-Disposition: inline In-Reply-To: <1305215624.2575.52.camel@mulgrave.site> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, May 12, 2011 at 10:53:44AM -0500, James Bottomley wrote: > On Thu, 2011-05-12 at 09:04 -0500, James Bottomley wrote: > > On Thu, 2011-05-12 at 14:13 +0300, Pekka Enberg wrote: > > > On 5/12/11 1:34 AM, James Bottomley wrote: > > > > On Wed, 2011-05-11 at 15:28 -0700, David Rientjes wrote: > > > >> On Wed, 11 May 2011, James Bottomley wrote: > > > >> > > > >>> OK, I confirm that I can't seem to break this one. No hangs visible, > > > >>> even when loading up the system with firefox, evolution, the usual > > > >>> massive untar, X and even a distribution upgrade. > > > >>> > > > >>> You can add my tested-by > > > >>> > > > >> Your system still hangs with patches 1 and 2 only? > > > > Yes, but only once in all the testing. With patches 1 and 2 the hang is > > > > much harder to reproduce, but it still seems to be present if I hit it > > > > hard enough. > > > > > > Patches 1-2 look reasonable to me. I'm not completely convinced of patch > > > 3, though. Why are we seeing these problems now? This has been in > > > mainline for a long time already. Shouldn't we fix kswapd? > > > > So I'm open to this. The hang occurs when kswapd races around in > > shrink_slab and never exits. It looks like there's a massive number of > > wakeups triggering this, but we haven't been able to diagnose it > > further. turning on PREEMPT gets rid of the hang, so I could try to > > reproduce with PREEMPT and turn on tracing. The problem so far has been > > that the number of events is so huge that the trace buffer only captures > > a few microseconds of output. > > OK, here's the trace from a PREEMPT kernel (2.6.38.6) when kswapd hits > 99% and stays there. I've only enabled the vmscan tracepoints to try > and get a longer run. It mosly looks like kswapd waking itself, but > there might be more in there that mm trained eyes can see. > For 2.6.38.6, commit [2876592f: mm: vmscan: stop reclaim/compaction earlier due to insufficient progress if !__GFP_REPEAT] may also be needed if CONFIG_COMPACTION if set. -- Mel Gorman SUSE Labs