[PATCH -mm -v3 08/12] memcg, THP, swap: Support move mem cgroup charge for THP swapped out

[Huang, Ying]

From: Huang Ying <ying.huang@xxxxxxxxx>

PTE mapped THP (Transparent Huge Page) will be ignored when moving
memory cgroup charge.  But for THP which is in the swap cache, the
memory cgroup charge for the swap of a tail-page may be moved in
current implementation.  That isn't correct, because the swap charge
for all sub-pages of a THP should be moved together.  Following the
processing of the PTE mapped THP, the mem cgroup charge moving for the
swap entry for a tail-page of a THP is ignored too.

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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3df3c04d73ab..c2618bd8ebdd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4616,8 +4616,11 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
 		if (!ret || !target)
 			put_page(page);
 	}
-	/* There is a swap entry and a page doesn't exist or isn't charged */
-	if (ent.val && !ret &&
+	/*
+	 * There is a swap entry and a page doesn't exist or isn't charged.
+	 * But we cannot move a tail-page in a THP.
+	 */
+	if (ent.val && !ret && (!page || !PageTransCompound(page)) &&
 	    mem_cgroup_id(mc.from) == lookup_swap_cgroup_id(ent)) {
 		ret = MC_TARGET_SWAP;
 		if (target)
-- 
2.13.2