linux-kernel - Re: [PATCH 5/7] mm: memcontrol: simplify the logic of objcg pinning memcg

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Date:   Tue, 13 Apr 2021 07:16:58 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com
Subject: Re: [PATCH 5/7] mm: memcontrol: simplify the logic of objcg pinning memcg

On Mon, Apr 12, 2021 at 11:58 PM Muchun Song <songmuchun@...edance.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@...edance.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

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