linux-kernel - [PATCH v2 2/3] mm/memcg: remove rcu locking for lock_page

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Date:   Tue, 22 Dec 2020 13:20:52 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     hughd@...gle.com
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] 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 Dickin's polished the commit log, Thanks a lot!

Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: cgroups@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/memcontrol.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8d400efc81b9..0af13c4fe4b3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1356,10 +1356,8 @@ struct lruvec *lock_page_lruvec(struct page *page)
 	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);
 
@@ -1371,10 +1369,8 @@ struct lruvec *lock_page_lruvec_irq(struct page *page)
 	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);
 
@@ -1386,10 +1382,8 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags)
 	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);
 
-- 
2.29.GIT