[065/173] mm/memcg: remove rcu locking for lock_page_lruvec function series

Commit Message

Andrew Morton Feb. 24, 2021, 8:03 p.m. UTC

From: Alex Shi <[e-mail]>
Subject: mm/memcg: remove rcu locking for lock_page_lruvec function series

lock_page_lruvec() and its variants used rcu_read_lock() with the
intention of safeguarding against the mem_cgroup being destroyed
concurrently; but so long as they are called under the specified
conditions (as they are), there is no way for the page's mem_cgroup to be
destroyed.  Delete the unnecessary rcu_read_lock() and _unlock().

Hugh Dickins polished the commit log.  Thanks a lot!

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Alex Shi <[e-mail]>
Acked-by: Hugh Dickins <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Vladimir Davydov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/memcontrol.c |    6 ------
 1 file changed, 6 deletions(-)

Patch

--- a/mm/memcontrol.c~mm-memcg-remove-rcu-locking-for-lock_page_lruvec-function-series
+++ a/mm/memcontrol.c
@@ -1357,10 +1357,8 @@  struct lruvec *lock_page_lruvec(struct p
 	struct lruvec *lruvec;
 	struct pglist_data *pgdat = page_pgdat(page);
 
-	rcu_read_lock();
 	lruvec = mem_cgroup_page_lruvec(page, pgdat);
 	spin_lock(&lruvec->lru_lock);
-	rcu_read_unlock();
 
 	lruvec_memcg_debug(lruvec, page);
 
@@ -1372,10 +1370,8 @@  struct lruvec *lock_page_lruvec_irq(stru
 	struct lruvec *lruvec;
 	struct pglist_data *pgdat = page_pgdat(page);
 
-	rcu_read_lock();
 	lruvec = mem_cgroup_page_lruvec(page, pgdat);
 	spin_lock_irq(&lruvec->lru_lock);
-	rcu_read_unlock();
 
 	lruvec_memcg_debug(lruvec, page);
 
@@ -1387,10 +1383,8 @@  struct lruvec *lock_page_lruvec_irqsave(
 	struct lruvec *lruvec;
 	struct pglist_data *pgdat = page_pgdat(page);
 
-	rcu_read_lock();
 	lruvec = mem_cgroup_page_lruvec(page, pgdat);
 	spin_lock_irqsave(&lruvec->lru_lock, *flags);
-	rcu_read_unlock();
 
 	lruvec_memcg_debug(lruvec, page);