linux-kernel - Re: [BUG] fatal hang untarring 90GB file, possibly writeback related.

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Date:	Thu, 28 Apr 2011 09:49:43 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Colin Ian King <colin.king.lkml@...il.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>
Subject: Re: [BUG] fatal hang untarring 90GB file, possibly writeback
 related.

On Thu, 2011-04-28 at 08:29 -0400, Chris Mason wrote:
> Excerpts from Colin Ian King's message of 2011-04-28 07:36:30 -0400:
> > 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.
> 
> Well, that's really interesting.  I tried with compaction on here and
> couldn't trigger it, but this (very very lightly) tested patch might
> help.
> 
> It moves the writeout throttle before the goto restart, and also makes
> sure we do at least one cond_resched before we loop.

It seems to take longer, but with a PREEMPT kernel, kswapd eventually
shoots up to 99% during the tar.

James


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