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:

quoted

On 11/02/2012 11:53 AM, Jiri Slaby wrote:

quoted

On 11/02/2012 11:44 AM, Zdenek Kabelac wrote:

quoted

quoted

quoted

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 [off-list ref]
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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