Re: kswapd consumes 100% CPU when highest zone is small

[Jerry Lee <leisurelysw24@gmail.com>]

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On 3 March 2016 at 16:22, Michal Hocko <mhocko@kernel.org> wrote:

> On Thu 03-03-16 10:23:03, Jerry Lee wrote:
> > On 3 March 2016 at 01:36, Michal Hocko <mhocko@kernel.org> wrote:
> >
> > > On Wed 02-03-16 14:20:38, Jerry Lee wrote:
> [...]
> > > > Is there anything I could do to totally get rid of the problem?
> > >
> > > I would try to sacrifice those few megs and get rid of zone normal
> > > completely. AFAIR mem=4G should limit the max_pfn to 4G so DMA32 should
> > > cover the shole memory.
> > >
> >
> > I came up with a patch that seem to work well on my system.  But, I
> > am afraid that it breaks the rule that all zones must be balanced for
> > order-0 request and It may cause some other side-effect?  I thought
> > that the patch is just a workaround (a bad one) and not a cure-all.
>
> One thing I haven't noticed previously is that you are running on the 3.12
> kernel. I vaguely remember there were some fixes for small zones. Not
> sure it would work for such a small zone but it would be worth trying I
> guess. Could you retest with 4.4?
>

Hi,

Thanks for the quick feedback!

Before sending a mail to linux-mm, I found that there were discussions and
fixes for the small zone as you remember:
https://lkml.org/lkml/2011/6/24/161 .
However, the fixes is kind of old and should be already included into the
current kernel version.  Speaking of retesting the issue with kernel-4.4,
it's
a bit hard for my right now because there are some customized hardware and
drivers on my system but I could give it a try.

BTW, there are some information I forgot to mention before.  Originally, I
use
kernel-3.4 on my system without the kswapd issue.  After upgrading to
linux-3.12.x, the issue occur.  In addition, I found that there are other
people
encountering the same problem even linux-4.x are used. [1] The idea to
increase the value of min_free_kbytes comes from the post. [1]

[1] https://github.com/GalliumOS/galliumos-distro/issues/52

Anyway, thanks again for your help and suggestion!

- Jerry



> --
> Michal Hocko
> SUSE Labs
>

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