From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: memcontrol: fix page charging in page replacement Patch series "memcontrol code cleanup and simplification", v3. This patch (of 8): The pages aren't accounted at the root level, so do not charge the page to the root memcg in page replacement. Although we do not display the value (mem_cgroup_usage) so there shouldn't be any actual problem, but there is a WARN_ON_ONCE in the page_counter_cancel(). Who knows if it will trigger? So it is better to fix it. Link: https://lkml.kernel.org/r/20210417043538.9793-1-songmuchun@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20210417043538.9793-2-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Roman Gushchin <guro@xxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-fix-page-charging-in-page-replacement +++ a/mm/memcontrol.c @@ -6984,9 +6984,11 @@ void mem_cgroup_migrate(struct page *old /* Force-charge the new page. The old one will be freed soon */ nr_pages = thp_nr_pages(newpage); - page_counter_charge(&memcg->memory, nr_pages); - if (do_memsw_account()) - page_counter_charge(&memcg->memsw, nr_pages); + if (!mem_cgroup_is_root(memcg)) { + page_counter_charge(&memcg->memory, nr_pages); + if (do_memsw_account()) + page_counter_charge(&memcg->memsw, nr_pages); + } css_get(&memcg->css); commit_charge(newpage, memcg); _
