Re: [PATCH] fs: buffer: use raw page_memcg() on locked page

[Shakeel Butt]

On Tue, Feb 9, 2021 at 11:01 AM Johannes Weiner <hannes@xxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>