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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Thu, 30 Mar 2023 00:55:17 -0700
Message-ID: <CAJD7tkZfexGoyZx0ormVzp_KkYmOczxBPfFaffKqd_TD4gvGCg@mail.gmail.com>
Subject: Re: [PATCH v2 7/9] workingset: memcg: sleep when flushing stats in workingset_refault()
To:     Michal Hocko <mhocko@suse.com>
Cc:     Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Vasily Averin <vasily.averin@linux.dev>,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        bpf@vger.kernel.org
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On Thu, Mar 30, 2023 at 12:50=E2=80=AFAM Michal Hocko <mhocko@suse.com> wro=
te:
>
> On Thu 30-03-23 00:42:36, Yosry Ahmed wrote:
> > On Thu, Mar 30, 2023 at 12:39=E2=80=AFAM Michal Hocko <mhocko@suse.com>=
 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 a=
n
> > > > 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.
>
> Right you are, my bad I have misread the intention here.
>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

>
> --
> Michal Hocko
> SUSE Labs