Re: [PATCH] mm/memcontrol: fix warning in mem_cgroup_page_lruvec()

From: Chris Down
Date: Wed Jan 06 2021 - 11:20:33 EST

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@xxxxxxxxxx>


Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>