From: James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0
Date: Thu, 12 May 2011 15:04:12 -0500
Message-ID: <1305230652.2575.72.camel@mulgrave.site>
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Cc: Christoph Lameter <cl@linux.com>, Mel Gorman <mgorman@suse.de>, Andrew
 Morton <akpm@linux-foundation.org>, Colin King <colin.king@canonical.com>,
 Raghavendra D Prabhu <raghu.prabhu13@gmail.com>, Jan Kara <jack@suse.cz>,
 Chris Mason <chris.mason@oracle.com>, Rik van Riel <riel@redhat.com>,
 Johannes Weiner <hannes@cmpxchg.org>, linux-fsdevel
 <linux-fsdevel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
 linux-kernel <linux-kernel@vger.kernel.org>, linux-ext4
 <linux-ext4@vger.kernel.org>
To: Pekka Enberg <penberg@kernel.org>
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On Thu, 2011-05-12 at 14:44 -0500, James Bottomley wrote:
> On Thu, 2011-05-12 at 13:37 -0500, James Bottomley wrote:
> > On Thu, 2011-05-12 at 18:55 +0300, Pekka Enberg wrote:
> > > On Thu, 2011-05-12 at 10:43 -0500, James Bottomley wrote:
> > > > However, since you admit even you see problems, let's concentrate on
> > > > fixing them rather than recriminations?
> > > 
> > > Yes, please. So does dropping max_order to 1 help?
> > > PAGE_ALLOC_COSTLY_ORDER is set to 3 in 2.6.39-rc7.
> > 
> > Just booting with max_slab_order=1 (and none of the other patches
> > applied) I can still get the machine to go into kswapd at 99%, so it
> > doesn't seem to make much of a difference.
> > 
> > Do you want me to try with the other two patches and max_slab_order=1?
> 
> OK, so patches 1 + 2 plus setting slub_max_order=1 still manages to
> trigger the problem (kswapd spinning at 99%).  This is still with
> PREEMPT; it's possible that non-PREEMPT might be better, so I'll try
> patches 1+2+3 with PREEMPT just to see if the perturbation is caused by
> it.

Confirmed, I'm afraid ... I can trigger the problem with all three
patches under PREEMPT.  It's not a hang this time, it's just kswapd
taking 100% system time on 1 CPU and it won't calm down after I unload
the system.

James


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