linux-kernel - Re: iotop: khugepaged at 99.99% (2.6.38.3)

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Message-ID: <20110504143842.GK7838@random.random>
Date:	Wed, 4 May 2011 16:38:42 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Thomas Sattler <tsattler@....de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: iotop: khugepaged at 99.99% (2.6.38.3)

Hello Thomas,

On Wed, May 04, 2011 at 02:20:04PM +0200, Thomas Sattler wrote:
> Different machine (kernel 2.6.38.2) 4x SYSRQ+l
> 
>    http://pastebin.com/raw.php?i=B2XeVyz6
>     (URL should be valid for one month)
> 
> Since this is a DualCore machine, it is still
> quite usable. I'll try to keep it running, in
> case you need more details.
> 
> BTW: I haven't seen the problem with 2.6.38.4
> so far. May have been fixed in the meantime?

There's no sign of khugepaged in the traces :( and one of the two cpu
is always idle (the other is often idle too). Maybe khugepaged was
stuck in D state and that is shown as 100% load for iotop? Please next
time can you run SYSRQ+t too in addition of SYSRQ+l? (I should have
suggested it right away but I thought khugepaged was running at 100%
cpu load and sysrq+t wouldn't have been as interesting in that
case). You can run also a "ps xal" to see the actual scheduler task
state. I suggest to stay at .2 if it reproduces it more easily.

If we understand what it is, it'll be easy to tell if it was already
fixed in 2.6.38.4 but I doubt unless it's not related to MM.

Thanks a lot for the help,
Andrea
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