[PATCH v3 1/8] mm: memcontrol: fix page charging in page replacement

From: Muchun Song <songmuchun@bytedance.com>
To: guro@fb.com, hannes@cmpxchg.org, mhocko@kernel.org,
	akpm@linux-foundation.org, shakeelb@google.com,
	vdavydov.dev@gmail.com
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	duanxiongchun@bytedance.com,
	Muchun Song <songmuchun@bytedance.com>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH v3 1/8] mm: memcontrol: fix page charging in page replacement
Date: Sat, 17 Apr 2021 12:35:31 +0800	[thread overview]
Message-ID: <20210417043538.9793-2-songmuchun@bytedance.com> (raw)
In-Reply-To: <20210417043538.9793-1-songmuchun@bytedance.com>

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@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>
---
 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

