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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 14 Aug 2018 17:54:13 -0700
Message-ID: <CALvZod4qhJA3NHnV_cTO0XEH1d4u62vxwug707sti7cZL6bgPw@mail.gmail.com>
Subject: Re: [RFC PATCH 2/2] mm: drain memcg stocks on css offlining
To:     Roman Gushchin <guro@fb.com>
Cc:     Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        kernel-team@fb.com, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, koct9i@gmail.com,
        Tejun Heo <tj@kernel.org>
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On Tue, Aug 14, 2018 at 5:36 PM Roman Gushchin <guro@fb.com> wrote:
>
> Memcg charge is batched using per-cpu stocks, so an offline memcg
> can be pinned by a cached charge up to a moment, when a process
> belonging to some other cgroup will charge some memory on the same
> cpu. In other words, cached charges can prevent a memory cgroup
> from being reclaimed for some time, without any clear need.
>
> Let's optimize it by explicit draining of all stocks on css offlining.
> As draining is performed asynchronously, and is skipped if any
> parallel draining is happening, it's cheap.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>

Seems reasonable.

Reviewed-by: Shakeel Butt <shakeelb@google.com>

> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Tejun Heo <tj@kernel.org>
> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4e3c1315b1de..cfb64b5b9957 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4575,6 +4575,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>         memcg_offline_kmem(memcg);
>         wb_memcg_offline(memcg);
>
> +       drain_all_stock(memcg);
> +
>         mem_cgroup_id_put(memcg);
>  }
>
> --
> 2.14.4
>