[PATCH v18 12/32] mm/memcg: optimize mem_cgroup_page_lruvec

[Alex Shi]

From: Hugh Dickins <hughd@xxxxxxxxxx>

Add READ_ONCE on page->mem_cgroup, since we will check it later.
Also the page should not be PageTail(page), so add a check.

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
---
 mm/memcontrol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 505f54087e82..65c1e873153e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1321,7 +1321,8 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
 		goto out;
 	}
 
-	memcg = page->mem_cgroup;
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	memcg = READ_ONCE(page->mem_cgroup);
 	/* Readahead page is charged too, to see if other page uncharged */
 	VM_WARN_ON_ONCE_PAGE(!memcg, page);
 	if (!memcg)
-- 
1.8.3.1