linux-kernel - Re: [RFC PATCH v2 02/18] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from

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Message-ID: <CALvZod5Z4r7RyU-zQdWBUn8bKibviXrfbyqVpgmO_e6VDjBHCg@mail.gmail.com>
Date:   Sat, 10 Apr 2021 10:47:08 -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, Balbir Singh <bsingharora@...il.com>,
        Yang Shi <shy828301@...il.com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Dan Schatzberg <schatzberg.dan@...il.com>
Subject: Re: [RFC PATCH v2 02/18] mm: memcontrol: bail out early when !mm in get_mem_cgroup_from_mm

On Fri, Apr 9, 2021 at 5:32 AM Muchun Song <songmuchun@...edance.com> wrote:
>
> When mm is NULL, we do not need to hold rcu lock and call css_tryget for
> the root memcg. And we also do not need to check !mm in every loop of
> while. So bail out early when !mm.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

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