[v4 PATCH 2/4] mm: move mem_cgroup_uncharge out of __page_cache_release()

[Yang Shi]

The later patch would make THP deferred split shrinker memcg aware, but
it needs page->mem_cgroup information in THP destructor, which is called
after mem_cgroup_uncharge() now.

So, move mem_cgroup_uncharge() from __page_cache_release() to compound
page destructor, which is called by both THP and other compound pages
except HugeTLB.  And call it in __put_single_page() for single order
page.

Suggested-by: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 1 +
 mm/swap.c       | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6c9cf1e..53a7a6c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -624,6 +624,7 @@ static void bad_page(struct page *page, const char *reason,
 
 void free_compound_page(struct page *page)
 {
+	mem_cgroup_uncharge(page);
 	__free_pages_ok(page, compound_order(page));
 }
 
diff --git a/mm/swap.c b/mm/swap.c
index 7ede3ed..170a725 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -71,12 +71,12 @@ static void __page_cache_release(struct page *page)
 		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
 	}
 	__ClearPageWaiters(page);
-	mem_cgroup_uncharge(page);
 }
 
 static void __put_single_page(struct page *page)
 {
 	__page_cache_release(page);
+	mem_cgroup_uncharge(page);
 	free_unref_page(page);
 }
 
-- 
1.8.3.1