linux-kernel - Re: kswapd0: excessive CPU usage

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Date:	Wed, 31 Oct 2012 15:04:38 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Thorsten Leemhuis <fedora@...mhuis.info>
Cc:	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>
Subject: Re: kswapd0: excessive CPU usage

On Wed, Oct 31, 2012 at 12:25:13PM +0100, Thorsten Leemhuis wrote:
> On 30.10.2012 20:18, Mel Gorman wrote:
> >On Mon, Oct 29, 2012 at 11:52:03AM +0100, Thorsten Leemhuis wrote:
> >>On 15.10.2012 13:09, Mel Gorman wrote:
> >>>On Mon, Oct 15, 2012 at 11:54:13AM +0200, Jiri Slaby wrote:
> >>>>On 10/12/2012 03:57 PM, Mel Gorman wrote:
> >>>>>mm: vmscan: scale number of pages reclaimed by reclaim/compaction only in direct reclaim
> >>>>>Jiri Slaby reported the following:
> >[...]
> >>>>Yes, applying this instead of the revert fixes the issue as well.
> >>Just wondering, is there a reason why this patch wasn't applied to
> >>mainline? Did it simply fall through the cracks? Or am I missing
> >>something?
> >It's because a problem was reported related to the patch (off-list,
> >whoops). I'm waiting to hear if a second patch fixes the problem or not.
> 
> Anything in particular I should look out for while testing?
> 

Excessive reclaim, high CPU usage by kswapd, processes getting stick in
isolate_migratepages or isolate_freepages.

> >>I'm asking because I think I stil see the issue on
> >>3.7-rc2-git-checkout-from-friday. Seems Fedora rawhide users are
> >>hitting it, too:
> >>https://bugzilla.redhat.com/show_bug.cgi?id=866988
> >I like the steps to reproduce.
> 
> One of those cases where the bugzilla bug template was not very
> helpful or where it was not used as intended (you decide) :-)
> 

It wins at entertainment value if nothing else :)

> >Is step 3 profit?
> 
> Yes, but psst, don't tell anyone; step 4 (world domination! for
> real!) is also hidden to keep that part of the big plan a secret for
> now ;-)
> 

No doubt it's the default private comment #1 !

> >>Or are we seeing something different which just looks similar?  I can
> >>test the patch if it needs further testing, but from the discussion
> >>I got the impression that everything is clear and the patch ready
> >>for merging.
> >It could be the same issue. Can you test with the "mm: vmscan: scale
> >number of pages reclaimed by reclaim/compaction only in direct reclaim"
> >patch and the following on top please?
> 
> Built a vanilla mainline kernel with those two patches and installed
> it on the machine where I was seeing problems high kswapd0 load on
> 3.7-rc3. Ran it an hour yesterday and a few hours today; seems the
> patches fix the issue for me as kswapd behaves:
> 
> $ LC_ALL=C ps -aux | grep 'kswapd'
> root       62  0.0  0.0      0     0 ?      S    Oct30   0:05 [kswapd0]
> 
> So everything is looking fine again so far thx to the two patches
> -- hopefully it stays that way even after hitting "send" in my
> mailer in a few seconds.
> 

Ok, great. Keep an eye on it please. If Jiri Slaby reports similar
success then I'll collapse the two patches together and resend to
Andrew.

Thanks.

-- 
Mel Gorman
SUSE Labs
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