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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/1608614453-10739-2-git-send-email-alex.shi@linux.alibaba.com
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
master
Alex Shi 2021-02-24 12:03:51 -08:00 committed by Linus Torvalds
parent d7e3aba583
commit f9b1038ebc
1 changed files with 0 additions and 6 deletions
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6
mm/memcontrol.c
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@ -1357,10 +1357,8 @@ 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);
@ -1372,10 +1370,8 @@ 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);
@ -1387,10 +1383,8 @@ 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);