linux-kernel - Re: [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag

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Date:   Fri, 2 Oct 2020 12:03:50 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...com
Subject: Re: [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag

On Thu, Oct 01, 2020 at 01:27:13PM -0400, Johannes Weiner <hannes@...xchg.org> wrote:
> The activation code is the only path where page migration is not
> excluded. Because unlike with page state statistics, we don't really
> mind a race when counting an activation event.
Thanks for the explanation. I see why the accessor trio is justified.

> I do think there is a bug, though: mem_cgroup_move_account() should
> use WRITE_ONCE() on page->mem_cgroup.
If this were a bug, wouldn't be the proper approach
rcu_assign_pointer()/rcu_dereference() pair?

Michal

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