linux-kernel - Re: kswapd0: excessive CPU usage

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Date:	Thu, 08 Nov 2012 22:22:05 -0600
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Jiri Slaby <jslaby@...e.cz>
CC:	Mel Gorman <mgorman@...e.de>, Zdenek Kabelac <zkabelac@...hat.com>,
	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 11/02/2012 02:45 PM, Jiri Slaby wrote:
> On 11/02/2012 11:53 AM, Jiri Slaby wrote:
>> On 11/02/2012 11:44 AM, Zdenek Kabelac wrote:
>>>>> Yes, applying this instead of the revert fixes the issue as well.
>>>
>>> I've applied this patch on 3.7.0-rc3 kernel - and I still see excessive
>>> CPU usage - mainly  after  suspend/resume
>>>
>>> Here is just simple  kswapd backtrace from running kernel:
>>
>> Yup, this is what we were seeing with the former patch only too. Try to
>> apply the other one too:
>> https://patchwork.kernel.org/patch/1673231/
>>
>> For me I would say, it is fixed by the two patches now. I won't be able
>> to report later, since I'm leaving to a conference tomorrow.
> 
> Damn it. It recurred right now, with both patches applied. After I
> started a java program which consumed some more memory. Though there are
> still 2 gigs free, kswap is spinning:
> [<ffffffff810b00da>] __cond_resched+0x2a/0x40
> [<ffffffff811318a0>] shrink_slab+0x1c0/0x2d0
> [<ffffffff8113478d>] kswapd+0x66d/0xb60
> [<ffffffff810a25d0>] kthread+0xc0/0xd0
> [<ffffffff816aa29c>] ret_from_fork+0x7c/0xb0
> [<ffffffffffffffff>] 0xffffffffffffffff

I'm also hitting this issue in v3.7-rc4.  It appears that the last
release not effected by this issue was v3.3.  Bisecting the changes
included for v3.4-rc1 showed that this commit introduced the issue:

fe2c2a106663130a5ab45cb0e3414b52df2fff0c is the first bad commit
commit fe2c2a106663130a5ab45cb0e3414b52df2fff0c
Author: Rik van Riel <riel@...hat.com>
Date:   Wed Mar 21 16:33:51 2012 -0700

    vmscan: reclaim at order 0 when compaction is enabled
...

This is plausible since the issue seems to be in the kswapd + compaction
realm.  I've yet to figure out exactly what about this commit results in
kswapd spinning.

I would be interested if someone can confirm this finding.

--
Seth

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