Re: [PATCH v2 7/9] workingset: memcg: sleep when flushing stats in workingset_refault()

[Yosry Ahmed]

On Thu, Mar 30, 2023 at 12:39 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Tue 28-03-23 22:16:42, Yosry Ahmed wrote:
> > In workingset_refault(), we call
> > mem_cgroup_flush_stats_atomic_ratelimited() to flush stats within an
> > RCU read section and with sleeping disallowed. Move the call above
> > the RCU read section and allow sleeping to avoid unnecessarily
> > performing a lot of work without sleeping.
>
> Could you say few words why the flushing is done before counters are
> updated rather than after (the RCU section)?

It's not about the counters that are updated, it's about the counters
that we read. Stats readers do a flush first to read accurate stats.
We flush before a read, not after an update.

> --
> Michal Hocko
> SUSE Labs