linux-kernel - Re: 2.6.21-rc3-mm1

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Date:	Fri, 16 Mar 2007 07:43:51 +0100
From:	Mariusz Kozlowski <m.kozlowski@...land.pl>
To:	Mel Gorman <mel@...net.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.21-rc3-mm1

Hello Mel,

> > > > > 	Today after +- 24h of uptime I found some more page allocation
> > > > > failures ('eth1: Can't allocate skb for Rx'). You'll find more here:
> > > > > 
> > > > > http://tuxland.pl/misc/2.6.21-rc3-mm1-page-allocation-failure.txt
> > > > > 
> > > > > System wasn't doing anything unusual, as usual ;-) X, some p2p 
> > > > > software, firefox+flash playing music.
> > > > 
> > > > Do other kernels do this, or is 2.6.21-rc3-mm1 worse?
> > > > 
> > > > It is of course a non-fatal problem and will inevitably happen sometimes,
> > > > but we would like the VM to be able to minimise the occurrence of this
> > > > problem.
> > > 
> > > Mariusz, I would be interested in finding out if this problem still occurs when
> > > you set min_free_kbytes to 16384 via /proc/sys/vm/min_free_kbytes. I understand
> > > that the problem is not easily reproduced and requiring configuration changes
> > > is far from ideal but it'd allow me to find out if options 2 or 3 below make
> > > sense in advance.
> > 
> > After a few hours I can confirm that this happens with 
> > 
> > $ cat /proc/sys/vm/min_free_kbytes 
> > 16384
> > 
> > as well. See the syslog output below. Feel free to mail me to do some more tests.
> 
> Ok, great. Well, not great because it's broken, but I know what's going
> on. I was able to reproduce the problem based on your report on my desktop
> and put together a fix for it. Full regression tests are still running but
> it should be in good enough state for you to test.
> 
> Without this patch, I got allocation failures within 15 minutes by stressing
> the machine. With the patch below, it's been up an hour and 15 minutes and
> I'm seeing no problems so far. Will keep the machine running a few days to
> see what happens.
> 

[...]
 
> Mariusz, please try the following patch. It should not be necessary to
> adjust your min_free_kbytes again but if you see a failure, please try
> with min_free_kbytes set to 16384. Thanks a lot.

Works for me. min_free_kbytes was left at default 2791. I left the laptop with
X + aMule + azureus + firefox&flash (playing music) + kernel compilation so
the box was pushed a bit. Uptime close to 9 hours and no page allocation
failures. I leave it running some more. If anything pops out you'll know it :-)

Thanks,

	Mariusz Kozlowski
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