[PATCH 08/18] mm: memcontrol: prepare cgroup vmstat infrastructure for native anon counters

[Johannes Weiner <hannes@cmpxchg.org>]

Anonymous compound pages can be mapped by ptes, which means that if we
want to track NR_MAPPED_ANON, NR_ANON_THPS on a per-cgroup basis, we
have to be prepared to see tail pages in our accounting functions.

Make mod_lruvec_page_state() and lock_page_memcg() deal with tail
pages correctly, namely by redirecting to the head page which has the
page->mem_cgroup set up.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 5 +++--
 mm/memcontrol.c            | 9 ++++++---
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5e8b0e38f145..5a1b5a7b7728 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -711,16 +711,17 @@ static inline void mod_lruvec_state(struct lruvec *lruvec,
 static inline void __mod_lruvec_page_state(struct page *page,
 					   enum node_stat_item idx, int val)
 {
+	struct page *head = compound_head(page); /* rmap on tail pages */
 	pg_data_t *pgdat = page_pgdat(page);
 	struct lruvec *lruvec;
 
 	/* Untracked pages have no memcg, no lruvec. Update only the node */
-	if (!page->mem_cgroup) {
+	if (!head->mem_cgroup) {
 		__mod_node_page_state(pgdat, idx, val);
 		return;
 	}
 
-	lruvec = mem_cgroup_lruvec(page->mem_cgroup, pgdat);
+	lruvec = mem_cgroup_lruvec(head->mem_cgroup, pgdat);
 	__mod_lruvec_state(lruvec, idx, val);
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ac6f2b073a5a..e9e22c86a118 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1979,6 +1979,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
  */
 struct mem_cgroup *lock_page_memcg(struct page *page)
 {
+	struct page *head = compound_head(page); /* rmap on tail pages */
 	struct mem_cgroup *memcg;
 	unsigned long flags;
 
@@ -1998,7 +1999,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
 	if (mem_cgroup_disabled())
 		return NULL;
 again:
-	memcg = page->mem_cgroup;
+	memcg = head->mem_cgroup;
 	if (unlikely(!memcg))
 		return NULL;
 
@@ -2006,7 +2007,7 @@ struct mem_cgroup *lock_page_memcg(struct page *page)
 		return memcg;
 
 	spin_lock_irqsave(&memcg->move_lock, flags);
-	if (memcg != page->mem_cgroup) {
+	if (memcg != head->mem_cgroup) {
 		spin_unlock_irqrestore(&memcg->move_lock, flags);
 		goto again;
 	}
@@ -2049,7 +2050,9 @@ void __unlock_page_memcg(struct mem_cgroup *memcg)
  */
 void unlock_page_memcg(struct page *page)
 {
-	__unlock_page_memcg(page->mem_cgroup);
+	struct page *head = compound_head(page);
+
+	__unlock_page_memcg(head->mem_cgroup);
 }
 EXPORT_SYMBOL(unlock_page_memcg);
 
-- 
2.26.0