linux-kernel - Re: kswapd hung tasks in 2.6.38-rc1

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Date:	Mon, 31 Jan 2011 14:40:16 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	CAI Qian <caiqian@...hat.com>
Cc:	linux-mm <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
	aarcange <aarcange@...hat.com>
Subject: Re: kswapd hung tasks in 2.6.38-rc1

On Mon, 2011-01-31 at 12:58 -0800, Dave Hansen wrote:
> On Thu, 2011-01-20 at 03:55 -0500, CAI Qian wrote:
> > When running LTP oom01 [1] testing, the allocation process stopped
> > processing right after starting to swap.
> 
> I'm seeing the same stuff, but on -rc2.  I thought it was
> transparent-hugepage-related, but I don't see much of a trace of it in
> the stack dumps.
> 
> http://sr71.net/~dave/ibm/config-v2.6.38-rc2
> 
> It happened to me as well around the time that things started to hit
> swap.

Still not a very good data point, but I ran a heavy swap load for an
hour or so without reproducing this.  But, it happened again after I
enabled transparent huge pages.  I managed to get a sysrq-t dump out of
it:

	http://sr71.net/~dave/ibm/2.6.38-rc2-hang-0.txt

khugepaged is one of the three running tasks.  Note, I set both its
sleep timeouts to zero to stress it out a bit.

I'll keep trying to reproduce without THP.

-- Dave

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