linux-kernel - Re: kswapd0: excessive CPU usage

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Date:	Mon, 12 Nov 2012 13:31:39 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Zdenek Kabelac <zkabelac@...hat.com>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Jiri Slaby <jslaby@...e.cz>, Valdis.Kletnieks@...edu,
	Jiri Slaby <jirislaby@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: kswapd0: excessive CPU usage

On Mon, Nov 12, 2012 at 02:13:20PM +0100, Zdenek Kabelac wrote:
> Dne 12.11.2012 13:19, Mel Gorman napsal(a):
> >On Sun, Nov 11, 2012 at 10:13:14AM +0100, Zdenek Kabelac wrote:
> >>Hmm,  so it's just took longer to hit the problem and observe kswapd0
> >>spinning on my CPU again - it's not as endless like before - but
> >>still it easily eats minutes - it helps to  turn off  Firefox or TB
> >>(memory hungry apps) so kswapd0 stops soon - and restart those apps
> >>again.
> >>(And I still have like >1GB of cached memory)
> >>
> >
> >I posted a "safe" patch that I believe explains why you are seeing what
> >you are seeing. It does mean that there will still be some stalls due to
> >THP because kswapd is not helping and it's avoiding the problem rather
> >than trying to deal with it.
> >
> >Hence, I'm also going to post this patch even though I have not tested
> >it myself. If you find it fixes the problem then it would be a
> >preferable patch to the revert. It still is the case that the
> >balance_pgdat() logic is in sort need of a rethink as it's pretty
> >twisted right now.
> >
> 
> 
> Should I apply them all together for 3.7-rc5 ?
> 
> 1) https://lkml.org/lkml/2012/11/5/308
> 2) https://lkml.org/lkml/2012/11/12/113
> 3) https://lkml.org/lkml/2012/11/12/151
> 

Not all together. Test either 1+2 or 1+3. 1+2 is the safer choice but
does nothing about THP stalls. 1+3 is a riskier version but depends on
me being correct on what the root cause of the problem you see it.

If both 1+2 and 1+3 work for you, I'd choose 1+3 for merging. If you only
have the time to test one combination then it would be preferred that you
test the safe option of 1+2.

Thanks.

-- 
Mel Gorman
SUSE Labs
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