linux-kernel - Re: [PATCH] mm/memcontrol: fix warning in mem_cgroup_page

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Date:   Wed, 6 Jan 2021 16:19:33 +0000
From:   Chris Down <chris@...isdown.name>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, Hui Su <sh_def@....com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/memcontrol: fix warning in mem_cgroup_page_lruvec()

Hugh Dickins writes:
>Boot a CONFIG_MEMCG=y kernel with "cgroup_disabled=memory" and you are
>met by a series of warnings from the VM_WARN_ON_ONCE_PAGE(!memcg, page)
>recently added to the inline mem_cgroup_page_lruvec().
>
>An earlier attempt to place that warning, in mem_cgroup_lruvec(), had
>been careful to do so after weeding out the mem_cgroup_disabled() case;
>but was itself invalid because of the mem_cgroup_lruvec(NULL, pgdat) in
>clear_pgdat_congested() and age_active_anon().
>
>Warning in mem_cgroup_page_lruvec() was once useful in detecting a KSM
>charge bug, so may be worth keeping: but skip if mem_cgroup_disabled().
>
>Fixes: 9a1ac2288cf1 ("mm/memcontrol:rewrite mem_cgroup_page_lruvec()")
>Signed-off-by: Hugh Dickins <hughd@...gle.com>

Thanks.

Acked-by: Chris Down <chris@...isdown.name>