[Devel] [PATCH rh7 4/9] tcache: Make tcache_lru_isolate() keep ni->lock less

[Kirill Tkhai]

Grab pool using RCU technics, and do not use ni->lock.
This refactors the function and will be used in further.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/tcache.c |   36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/mm/tcache.c b/mm/tcache.c
index f2a9f439afb..cecaf02b365 100644
--- a/mm/tcache.c
+++ b/mm/tcache.c
@@ -1031,31 +1031,51 @@ tcache_lru_isolate(int nid, struct page **pages, int nr_to_isolate)
 	int nr, nr_isolated = 0;
 	struct rb_node *rbn;
 
-	spin_lock_irq(&ni->lock);
+	rcu_read_lock();
 again:
 	rbn = rb_first(&ni->reclaim_tree);
-	if (!rbn)
+	if (!rbn) {
+		rcu_read_unlock();
 		goto out;
-
-	rb_erase(rbn, &ni->reclaim_tree);
-	RB_CLEAR_NODE(rbn);
+	}
 
 	pni = rb_entry(rbn, struct tcache_pool_nodeinfo, reclaim_node);
-	if (!tcache_grab_pool(pni->pool))
+	if (!tcache_grab_pool(pni->pool)) {
+		spin_lock_irq(&ni->lock);
+		if (!RB_EMPTY_NODE(rbn) && list_empty(&pni->lru)) {
+			rb_erase(rbn, &ni->reclaim_tree);
+			RB_CLEAR_NODE(rbn);
+		}
+		spin_unlock_irq(&ni->lock);
 		goto again;
+	}
+	rcu_read_unlock();
 
+	spin_lock_irq(&ni->lock);
 	spin_lock(&pni->lock);
 	nr = __tcache_lru_isolate(pni, pages, nr_to_isolate);
-	ni->nr_pages -= nr;
 	nr_isolated += nr;
 
+	if (!nr) {
+		spin_unlock(&pni->lock);
+		spin_unlock_irq(&ni->lock);
+		goto out_put;
+	}
+
+	ni->nr_pages -= nr;
+
+	if (!RB_EMPTY_NODE(rbn)) {
+		rb_erase(rbn, &ni->reclaim_tree);
+		RB_CLEAR_NODE(rbn);
+	}
 	if (!list_empty(&pni->lru))
 		__tcache_insert_reclaim_node(ni, pni);
 
 	spin_unlock(&pni->lock);
+	spin_unlock_irq(&ni->lock);
+out_put:
 	tcache_put_pool(pni->pool);
 out:
-	spin_unlock_irq(&ni->lock);
 	return nr_isolated;
 }