linux-ext4 - Re: [BUG] fatal hang untarring 90GB file, possibly writeback related.

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Date:	Fri, 6 May 2011 20:37:48 +0100
From:	Mel Gorman <mgorman@...ell.com>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Mel Gorman <mgorman@...e.de>, 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>
Subject: Re: [BUG] fatal hang untarring 90GB file, possibly writeback related.

On Fri, May 06, 2011 at 02:14:37PM -0500, James Bottomley wrote:
> On Fri, 2011-05-06 at 16:44 +0100, Mel Gorman wrote:
> > Colin and James: Did you happen to switch from SLAB to SLUB between
> > 2.6.37 and 2.6.38? My own tests were against SLAB which might be why I
> > didn't see the problem. Am restarting the tests with SLUB.
> 
> Aargh ... I'm an idiot.  I should have thought of SLUB immediately ...
> it's been causing oopses since debian switched to it.
> 
> So I recompiled the 2.6.38.4 stable kernel with SLAB instead of SLUB and
> the problem goes away ... at least from three untar runs on a loaded
> box ... of course it could manifest a few ms after I send this email ...
> 
> There are material differences, as well: SLAB isn't taking my system
> down to very low memory on the untar ... it's keeping about 0.5Gb listed
> as free.  SLUB took that to under 100kb, so it could just be that SLAB
> isn't wandering as close to the cliff edge?
> 

A comparison of watch-highorder.pl with SLAB and SLUB may be
enlightening as well as testing SLUB altering allocate_slab() to read

alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;

i.e. try adding the __GFP_NO_KSWAPD. My own tests are still in progress
but I'm still not seeing the problem. I'm installing Fedora on another
test machine at the moment to see if X and other applications have to be
running to pressure high-order allocations properly.

-- 
Mel Gorman
SUSE Labs
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