Re: kswapd0: excessive CPU usage

[Zdenek Kabelac]

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@xxxxxxxxxx>
> 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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