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@bytedance.com
Link: https://lkml.kernel.org/r/20210417043538.9793-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 70690fd..239f69e 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6984,9 +6984,11 @@ 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);