Date: Sun, 24 May 2015 17:24:40 -0400
From: Tejun Heo <tj@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, jack@suse.cz,
        hch@infradead.org, linux-fsdevel@vger.kernel.org, vgoyal@redhat.com,
        lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org,
        mhocko@suse.cz, clm@fb.com, fengguang.wu@intel.com,
        david@fromorbit.com, gthelen@google.com, khlebnikov@yandex-team.ru
Subject: Re: [PATCH 11/51] memcg: implement mem_cgroup_css_from_page()
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Hello,

On Fri, May 22, 2015 at 07:28:31PM -0400, Johannes Weiner wrote:
> replace_page_cache() can clear page->mem_cgroup even when the page
> still has references, so unfortunately you must hold the page lock
> when calling this function.
> 
> I haven't checked how you use this - chances are you always have the
> page locked anyways - but it probably needs a comment.

Hmmm... as replace_page_cache_page() is used only by fuse and fuse's
bdi doesn't go through the usual writeback accounting which is
necessary for cgroup writeback support anyway, so I don't think this
presents an actual problem.  I'll add a warning in
replace_page_cache_page() which triggers when it's used on a bdi which
has cgroup writeback enabled and add comments explaining what's going
on.

Thanks.

-- 
tejun
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