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.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/memcontrol.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 64ada9e650a5..f229de925aa5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6806,9 +6806,11 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
/* 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);
--
2.11.0
