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Date:	Thu, 28 Apr 2011 09:25:14 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Jan Kara <jack@...e.cz>, colin.king@...onical.com,
	Chris Mason <chris.mason@...cle.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>, mgorman@...ell.com
Subject: Re: [BUG] fatal hang untarring 90GB file, possibly writeback
 related.

On Thu, 2011-04-28 at 15:07 +0100, Mel Gorman wrote:
> On Thu, Apr 28, 2011 at 03:52:28PM +0200, Jan Kara wrote:
> > On Thu 28-04-11 12:36:30, Colin Ian King wrote:
> > > One more data point to add, I've been looking at an identical issue when
> > > copying large amounts of data.  I bisected this - and the lockups occur
> > > with commit 
> > > 3e7d344970673c5334cf7b5bb27c8c0942b06126 - before that I don't see the
> > > issue. With this commit, my file copy test locks up after ~8-10
> > > iterations, before this commit I can copy > 100 times and don't see the
> > > lockup.
> >   Adding Mel to CC, I guess he'll be interested. Mel, it seems this commit
> > of yours causes kswapd on non-preempt kernels spin for a *long* time...
> > 
> 
> I'm still thinking about the traces which do not point the finger
> directly at compaction per-se but it's possible that the change means
> kswapd is not reclaiming like it should be.
> 
> To test this theory, does applying
> [d527caf2: mm: compaction: prevent kswapd compacting memory to reduce
> CPU usage] help?

I can answer definitively no to this.  The upstream kernel I reproduced
this on has that patch included.

James



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