linux-kernel - Re: kswapd0: excessive CPU usage

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Date:	Wed, 31 Oct 2012 12:25:13 +0100
From:	Thorsten Leemhuis <fedora@...mhuis.info>
To:	Mel Gorman <mgorman@...e.de>
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 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?

>> 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) :-)

> 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 ;-)

>> 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.

CU
knurd
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