linux-kernel - Re: kswapd0: excessive CPU usage

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Date:	Fri, 09 Nov 2012 09:07:45 +0100
From:	Zdenek Kabelac <zkabelac@...hat.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Jiri Slaby <jslaby@...e.cz>, Mel Gorman <mgorman@...e.de>,
	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

Dne 9.11.2012 05:22, Seth Jennings napsal(a):
> 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
>


On my system 3.7-rc4 the problem seems to be effectively solved by revert 
patch: https://lkml.org/lkml/2012/11/5/308

i.e. in 2 days uptime kswapd0 eats 6 seconds which is IMHO ok - I'm not 
observing any busy loops on CPU with kswapd0.


Zdenek

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