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References: <20210413065153.63431-1-songmuchun@bytedance.com> <20210413065153.63431-6-songmuchun@bytedance.com>
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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 13 Apr 2021 07:16:58 -0700
Message-ID: <CALvZod4B3-OREkm2ZVGyueUcJRE2igTjhNHTE3nVDSzTVRDs6Q@mail.gmail.com>
Subject: Re: [PATCH 5/7] mm: memcontrol: simplify the logic of objcg pinning memcg
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     Roman Gushchin <guro@fb.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Xiongchun duan <duanxiongchun@bytedance.com>,
        fam.zheng@bytedance.com
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On Mon, Apr 12, 2021 at 11:58 PM Muchun Song <songmuchun@bytedance.com> wrote:
>
> The obj_cgroup_release() and memcg_reparent_objcgs() are serialized by
> the css_set_lock. We do not need to care about objcg->memcg being
> released in the process of obj_cgroup_release(). So there is no need
> to pin memcg before releasing objcg. Remove those pinning logic to
> simplfy the code.
>
> There are only two places that modifies the objcg->memcg. One is the
> initialization to objcg->memcg in the memcg_online_kmem(), another
> is objcgs reparenting in the memcg_reparent_objcgs(). It is also
> impossible for the two to run in parallel. So xchg() is unnecessary
> and it is enough to use WRITE_ONCE().
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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