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References: <20210209190126.97842-1-hannes@cmpxchg.org>
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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 9 Feb 2021 11:12:18 -0800
Message-ID: <CALvZod6jd5+H0jr8wyB_ivPcJzSYH-rCCQL64Hgg+D_wuAZZFg@mail.gmail.com>
Subject: Re: [PATCH] fs: buffer: use raw page_memcg() on locked page
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Michal Hocko <mhocko@suse.com>, Linux MM <linux-mm@kvack.org>,
        Cgroups <cgroups@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Team <kernel-team@fb.com>
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On Tue, Feb 9, 2021 at 11:01 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> alloc_page_buffers() currently uses get_mem_cgroup_from_page() for
> charging the buffers to the page owner, which does an rcu-protected
> page->memcg lookup and acquires a reference. But buffer allocation has
> the page lock held throughout, which pins the page to the memcg and
> thereby the memcg - neither rcu nor holding an extra reference during
> the allocation are necessary. Use a raw page_memcg() instead.
>
> This was the last user of get_mem_cgroup_from_page(), delete it.
>
> Reported-by: Muchun Song <songmuchun@bytedance.com>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

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