[PATCH -mm -v3 09/12] memcg, THP, swap: Avoid to duplicated charge THP in swap cache

[Huang, Ying]

From: Huang Ying <ying.huang@xxxxxxxxx>

For a THP (Transparent Huge Page), tail_page->mem_cgroup is NULL.  So
to check whether the page is charged already, we need to check the
head page.  This is not an issue before because it is impossible for a
THP to be in the swap cache before.  But after we add delaying
splitting THP after swapped out support, it is possible now.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c2618bd8ebdd..a627b0fd67ea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5407,7 +5407,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
 		 * in turn serializes uncharging.
 		 */
 		VM_BUG_ON_PAGE(!PageLocked(page), page);
-		if (page->mem_cgroup)
+		if (compound_head(page)->mem_cgroup)
 			goto out;
 
 		if (do_swap_account) {
-- 
2.13.2