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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 28 Feb 2022 14:46:44 -0800
Message-ID: <CALvZod61XyMJzrvU0Wvp8iWV878rZQYsa407RhoZYeiJV5j5SQ@mail.gmail.com>
Subject: Re: [PATCH] memcg: async flush memcg stats from perf sensitive codepaths
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Ivan Babrou <ivan@cloudflare.com>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Daniel Dao <dqminh@cloudflare.com>,
        stable <stable@vger.kernel.org>
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On Mon, Feb 28, 2022 at 10:46 AM Michal Koutn=C3=BD <mkoutny@suse.com> wrot=
e:
>
> On Fri, Feb 25, 2022 at 05:42:57PM -0800, Shakeel Butt <shakeelb@google.c=
om> wrote:
> > Yes, the right fix would be to optimize the flushing code (but that
> > would require more work/time). However I still think letting
> > performance critical code paths to skip the sync flush would be good
> > in general. So, if the current patch is not to your liking we can
> > remove mem_cgroup_flush_stats() from workingset_refault().
>
> What about flushing just the subtree of the memcg where the refault
> happens?
> It doesn't reduce the overall work and there's still full-tree
> cgroup_rstat_lock but it should make the chunks of work smaller
> durations more regular.
>

We can try that and I will send a patch to Ivan and Daniel to try on
their workload to see the real impact of targeted memcg flushing.
However I am not very optimistic about it.