linux-kernel - Re: [PATCH] fs: buffer: use raw page

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Message-ID: <20210209192001.GA524633@carbon.DHCP.thefacebook.com>
Date:   Tue, 9 Feb 2021 11:20:01 -0800
From:   Roman Gushchin <guro@...com>
To:     Johannes Weiner <hannes@...xchg.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <songmuchun@...edance.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>, <linux-mm@...ck.org>,
        <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH] fs: buffer: use raw page_memcg() on locked page

On Tue, Feb 09, 2021 at 02:01:26PM -0500, Johannes Weiner 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@...edance.com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Roman Gushchin <guro@...com>

Thanks!