Re: Regression in workingset_refault latency on 5.15

[Shakeel Butt <shakeelb@google.com>]

On Thu, Feb 24, 2022 at 9:34 AM Daniel Dao <dqminh@cloudflare.com> wrote:
>
[...]
> > Thanks for testing. At the moment I am suspecting the async worker is
> > not getting the CPU. Can you share your CONFIG_HZ setting? Also can you
> > try the following patch and see if that helps otherwise keep halving the
> > delay (i.e. 2HZ -> HZ -> HZ/2 -> ...) and find at what value the issue
> > you are seeing get resolved?
>
> We have CONFIG_HZ=1000. We can try to increase the frequency of async flush, but
> that seems like a not great bandaid. Is it possible to remove
> mem_cgroup_flush_stats()
> from workingset_refault, or at least scope it down to some targeted cgroup so
> we don't need to flush from root with potentially large sets of
> cgroups to walk ?

I actually wanted to know what would be the good frequency of rstat
flushing for your workload. I am not planning to propose to change the
default frequency.

Anyways I am thinking of introducing mem_cgroup_flush_stats_asyn()
which will schedule flush_memcg_stats_dwork() without delay. Let me
prepare the patch based on 5.15-stable for you to test.