Blk-throttle: update to use rbtree with leftmost node cached

As rbtree has native support of caching leftmost node,
i.e. rb_root_cached, no need to do the caching by ourselves.
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-throttle.c

@@ -84,8 +84,7 @@ struct throtl_service_queue {
 	 * RB tree of active children throtl_grp's, which are sorted by
 	 * their ->disptime.
 	 */
-	struct rb_root		pending_tree;	/* RB tree of active tgs */
-	struct rb_node		*first_pending;	/* first node in the tree */
+	struct rb_root_cached	pending_tree;	/* RB tree of active tgs */
 	unsigned int		nr_pending;	/* # queued in the tree */
 	unsigned long		first_pending_disptime;	/* disptime of the first tg */
 	struct timer_list	pending_timer;	/* fires on first_pending_disptime */
@@ -475,7 +474,7 @@ static void throtl_service_queue_init(struct throtl_service_queue *sq)
 {
 	INIT_LIST_HEAD(&sq->queued[0]);
 	INIT_LIST_HEAD(&sq->queued[1]);
-	sq->pending_tree = RB_ROOT;
+	sq->pending_tree = RB_ROOT_CACHED;
 	timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
 }
 
@@ -616,31 +615,23 @@ static void throtl_pd_free(struct blkg_policy_data *pd)
 static struct throtl_grp *
 throtl_rb_first(struct throtl_service_queue *parent_sq)
 {
+	struct rb_node *n;
 	/* Service tree is empty */
 	if (!parent_sq->nr_pending)
 		return NULL;
 
-	if (!parent_sq->first_pending)
-		parent_sq->first_pending = rb_first(&parent_sq->pending_tree);
-
-	if (parent_sq->first_pending)
-		return rb_entry_tg(parent_sq->first_pending);
-
+	n = rb_first_cached(&parent_sq->pending_tree);
+	WARN_ON_ONCE(!n);
+	if (!n)
 		return NULL;
-}
-
-static void rb_erase_init(struct rb_node *n, struct rb_root *root)
-{
-	rb_erase(n, root);
-	RB_CLEAR_NODE(n);
+	return rb_entry_tg(n);
 }
 
 static void throtl_rb_erase(struct rb_node *n,
 			    struct throtl_service_queue *parent_sq)
 {
-	if (parent_sq->first_pending == n)
-		parent_sq->first_pending = NULL;
-	rb_erase_init(n, &parent_sq->pending_tree);
+	rb_erase_cached(n, &parent_sq->pending_tree);
+	RB_CLEAR_NODE(n);
 	--parent_sq->nr_pending;
 }
 
@@ -658,11 +649,11 @@ static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
 static void tg_service_queue_add(struct throtl_grp *tg)
 {
 	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
-	struct rb_node **node = &parent_sq->pending_tree.rb_node;
+	struct rb_node **node = &parent_sq->pending_tree.rb_root.rb_node;
 	struct rb_node *parent = NULL;
 	struct throtl_grp *__tg;
 	unsigned long key = tg->disptime;
-	int left = 1;
+	bool leftmost = true;
 
 	while (*node != NULL) {
 		parent = *node;
@@ -672,15 +663,13 @@ static void tg_service_queue_add(struct throtl_grp *tg)
 			node = &parent->rb_left;
 		else {
 			node = &parent->rb_right;
-			left = 0;
+			leftmost = false;
 		}
 	}
 
-	if (left)
-		parent_sq->first_pending = &tg->rb_node;
-
 	rb_link_node(&tg->rb_node, parent, node);
-	rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);
+	rb_insert_color_cached(&tg->rb_node, &parent_sq->pending_tree,
+			       leftmost);
 }
 
 static void __throtl_enqueue_tg(struct throtl_grp *tg)