[085/192] mm: memcontrol: fix page charging in page replacement

Commit Message

Andrew Morton June 29, 2021, 2:37 a.m. UTC

From: Muchun Song <[e-mail]>
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/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Muchun Song <[e-mail]>
Acked-by: Johannes Weiner <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Acked-by: Roman Gushchin <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Cc: Vladimir Davydov <[e-mail]>
Cc: Xiongchun Duan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/memcontrol.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Patch

--- 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);