[PATCH v2 6/8] mm/lru: remove rcu_read_lock to fix performance regression

Alex Shi
2019-11-12T14:06:26Z

Intel 0day report there are performance regression on this patchset.
The detailed info points to rcu_read_lock + PROVE_LOCKING which causes
queued_spin_lock_slowpath waiting too long time to get lock.
Remove rcu_read_lock is safe here since we had a spinlock hold.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
include/linux/memcontrol.h | 29 ++++++++++++-----------------
1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2421b720d272..f869897a68f0 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1307,20 +1307,18 @@ static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
struct pglist_data *pgdat = page_pgdat(page);
struct lruvec *lruvec;

- rcu_read_lock();
+ if (!locked_lruvec)
+ goto lock;
+
lruvec = mem_cgroup_page_lruvec(page, pgdat);

- if (locked_lruvec == lruvec) {
- rcu_read_unlock();
+ if (locked_lruvec == lruvec)
return lruvec;
- }
- rcu_read_unlock();

- if (locked_lruvec)
- spin_unlock_irq(&locked_lruvec->lru_lock);
+ spin_unlock_irq(&locked_lruvec->lru_lock);

+lock:
lruvec = lock_page_lruvec_irq(page, pgdat);
-
return lruvec;
}

@@ -1331,21 +1329,18 @@ static inline struct lruvec *relock_page_lruvec_irqsave(struct page *page,
struct pglist_data *pgdat = page_pgdat(page);
struct lruvec *lruvec;

- rcu_read_lock();
+ if (!locked_lruvec)
+ goto lock;
+
lruvec = mem_cgroup_page_lruvec(page, pgdat);

- if (locked_lruvec == lruvec) {
- rcu_read_unlock();
+ if (locked_lruvec == lruvec)
return lruvec;
- }
- rcu_read_unlock();

- if (locked_lruvec)
- spin_unlock_irqrestore(&locked_lruvec->lru_lock,
- locked_lruvec->flags);
+ spin_unlock_irqrestore(&locked_lruvec->lru_lock, locked_lruvec->flags);

+lock:
lruvec = lock_page_lruvec_irqsave(page, pgdat);
-
return lruvec;
}

--
1.8.3.1