[PATCH v7 02/10] mm/memcg: fold lru_lock in lock_page_lru

[Alex Shi]

>From the commit_charge's explanations and mem_cgroup_commit_charge
comments, as well as call path when lrucare is ture, The lru_lock is
just to guard the task migration(which would be lead to move_account)
So it isn't needed when !PageLRU, and better be fold into PageLRU to
reduce lock contentions.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/memcontrol.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5b5f74cfd4d..0ad10caabc3d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2572,12 +2572,11 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
 
 static void lock_page_lru(struct page *page, int *isolated)
 {
-	pg_data_t *pgdat = page_pgdat(page);
-
-	spin_lock_irq(&pgdat->lru_lock);
 	if (PageLRU(page)) {
+		pg_data_t *pgdat = page_pgdat(page);
 		struct lruvec *lruvec;
 
+		spin_lock_irq(&pgdat->lru_lock);
 		lruvec = mem_cgroup_page_lruvec(page, pgdat);
 		ClearPageLRU(page);
 		del_page_from_lru_list(page, lruvec, page_lru(page));
@@ -2588,17 +2587,17 @@ static void lock_page_lru(struct page *page, int *isolated)
 
 static void unlock_page_lru(struct page *page, int isolated)
 {
-	pg_data_t *pgdat = page_pgdat(page);
 
 	if (isolated) {
+		pg_data_t *pgdat = page_pgdat(page);
 		struct lruvec *lruvec;
 
 		lruvec = mem_cgroup_page_lruvec(page, pgdat);
 		VM_BUG_ON_PAGE(PageLRU(page), page);
 		SetPageLRU(page);
 		add_page_to_lru_list(page, lruvec, page_lru(page));
+		spin_unlock_irq(&pgdat->lru_lock);
 	}
-	spin_unlock_irq(&pgdat->lru_lock);
 }
 
 static void commit_charge(struct page *page, struct mem_cgroup *memcg,
-- 
1.8.3.1