Btrfs: introduce a head ref rbtree

The way how we process delayed refs is
1) get a bunch of head refs,
2) pick up one head ref,
3) go one node back for any delayed ref updates.

The head ref is also linked in the same rbtree as the delayed ref is,
so in 1) stage, we have to walk one by one including not only head refs, but
delayed refs.

When we have a great number of delayed refs pending to process,
this'll cost time a lot.

Here we introduce a head ref specific rbtree, it only has head refs, so troubles
go away.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 74 insertions, 52 deletions

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index e4d467be2dd..9bbac6ddf41 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -161,35 +161,61 @@ static struct btrfs_delayed_ref_node *tree_insert(struct rb_root *root,
 	return NULL;
 }
 
+/* insert a new ref to head ref rbtree */
+static struct btrfs_delayed_ref_head *htree_insert(struct rb_root *root,
+						   struct rb_node *node)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent_node = NULL;
+	struct btrfs_delayed_ref_head *entry;
+	struct btrfs_delayed_ref_head *ins;
+	u64 bytenr;
+
+	ins = rb_entry(node, struct btrfs_delayed_ref_head, href_node);
+	bytenr = ins->node.bytenr;
+	while (*p) {
+		parent_node = *p;
+		entry = rb_entry(parent_node, struct btrfs_delayed_ref_head,
+				 href_node);
+
+		if (bytenr < entry->node.bytenr)
+			p = &(*p)->rb_left;
+		else if (bytenr > entry->node.bytenr)
+			p = &(*p)->rb_right;
+		else
+			return entry;
+	}
+
+	rb_link_node(node, parent_node, p);
+	rb_insert_color(node, root);
+	return NULL;
+}
+
 /*
  * find an head entry based on bytenr. This returns the delayed ref
  * head if it was able to find one, or NULL if nothing was in that spot.
  * If return_bigger is given, the next bigger entry is returned if no exact
  * match is found.
  */
-static struct btrfs_delayed_ref_node *find_ref_head(struct rb_root *root,
-				  u64 bytenr,
-				  struct btrfs_delayed_ref_node **last,
-				  int return_bigger)
+static struct btrfs_delayed_ref_head *
+find_ref_head(struct rb_root *root, u64 bytenr,
+	      struct btrfs_delayed_ref_head **last, int return_bigger)
 {
 	struct rb_node *n;
-	struct btrfs_delayed_ref_node *entry;
+	struct btrfs_delayed_ref_head *entry;
 	int cmp = 0;
 
 again:
 	n = root->rb_node;
 	entry = NULL;
 	while (n) {
-		entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
-		WARN_ON(!entry->in_tree);
+		entry = rb_entry(n, struct btrfs_delayed_ref_head, href_node);
 		if (last)
 			*last = entry;
 
-		if (bytenr < entry->bytenr)
+		if (bytenr < entry->node.bytenr)
 			cmp = -1;
-		else if (bytenr > entry->bytenr)
-			cmp = 1;
-		else if (!btrfs_delayed_ref_is_head(entry))
+		else if (bytenr > entry->node.bytenr)
 			cmp = 1;
 		else
 			cmp = 0;
@@ -203,12 +229,12 @@ again:
 	}
 	if (entry && return_bigger) {
 		if (cmp > 0) {
-			n = rb_next(&entry->rb_node);
+			n = rb_next(&entry->href_node);
 			if (!n)
 				n = rb_first(root);
-			entry = rb_entry(n, struct btrfs_delayed_ref_node,
-					 rb_node);
-			bytenr = entry->bytenr;
+			entry = rb_entry(n, struct btrfs_delayed_ref_head,
+					 href_node);
+			bytenr = entry->node.bytenr;
 			return_bigger = 0;
 			goto again;
 		}
@@ -246,6 +272,12 @@ static inline void drop_delayed_ref(struct btrfs_trans_handle *trans,
 				    struct btrfs_delayed_ref_node *ref)
 {
 	rb_erase(&ref->rb_node, &delayed_refs->root);
+	if (btrfs_delayed_ref_is_head(ref)) {
+		struct btrfs_delayed_ref_head *head;
+
+		head = btrfs_delayed_node_to_head(ref);
+		rb_erase(&head->href_node, &delayed_refs->href_root);
+	}
 	ref->in_tree = 0;
 	btrfs_put_delayed_ref(ref);
 	delayed_refs->num_entries--;
@@ -379,42 +411,35 @@ int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
 	int count = 0;
 	struct btrfs_delayed_ref_root *delayed_refs;
 	struct rb_node *node;
-	struct btrfs_delayed_ref_node *ref;
-	struct btrfs_delayed_ref_head *head;
+	struct btrfs_delayed_ref_head *head = NULL;
 
 	delayed_refs = &trans->transaction->delayed_refs;
-	if (start == 0) {
-		node = rb_first(&delayed_refs->root);
-	} else {
-		ref = NULL;
-		find_ref_head(&delayed_refs->root, start + 1, &ref, 1);
-		if (ref) {
-			node = &ref->rb_node;
-		} else
-			node = rb_first(&delayed_refs->root);
+	node = rb_first(&delayed_refs->href_root);
+
+	if (start) {
+		find_ref_head(&delayed_refs->href_root, start + 1, &head, 1);
+		if (head)
+			node = &head->href_node;
 	}
 again:
 	while (node && count < 32) {
-		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
-		if (btrfs_delayed_ref_is_head(ref)) {
-			head = btrfs_delayed_node_to_head(ref);
-			if (list_empty(&head->cluster)) {
-				list_add_tail(&head->cluster, cluster);
-				delayed_refs->run_delayed_start =
-					head->node.bytenr;
-				count++;
-
-				WARN_ON(delayed_refs->num_heads_ready == 0);
-				delayed_refs->num_heads_ready--;
-			} else if (count) {
-				/* the goal of the clustering is to find extents
-				 * that are likely to end up in the same extent
-				 * leaf on disk.  So, we don't want them spread
-				 * all over the tree.  Stop now if we've hit
-				 * a head that was already in use
-				 */
-				break;
-			}
+		head = rb_entry(node, struct btrfs_delayed_ref_head, href_node);
+		if (list_empty(&head->cluster)) {
+			list_add_tail(&head->cluster, cluster);
+			delayed_refs->run_delayed_start =
+				head->node.bytenr;
+			count++;
+
+			WARN_ON(delayed_refs->num_heads_ready == 0);
+			delayed_refs->num_heads_ready--;
+		} else if (count) {
+			/* the goal of the clustering is to find extents
+			 * that are likely to end up in the same extent
+			 * leaf on disk.  So, we don't want them spread
+			 * all over the tree.  Stop now if we've hit
+			 * a head that was already in use
+			 */
+			break;
 		}
 		node = rb_next(node);
 	}
@@ -426,7 +451,7 @@ again:
 		 * clusters.  start from the beginning and try again
 		 */
 		start = 0;
-		node = rb_first(&delayed_refs->root);
+		node = rb_first(&delayed_refs->href_root);
 		goto again;
 	}
 	return 1;
@@ -612,6 +637,7 @@ static noinline void add_delayed_ref_head(struct btrfs_fs_info *fs_info,
 		 */
 		kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
 	} else {
+		htree_insert(&delayed_refs->href_root, &head_ref->href_node);
 		delayed_refs->num_heads++;
 		delayed_refs->num_heads_ready++;
 		delayed_refs->num_entries++;
@@ -869,14 +895,10 @@ int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info,
 struct btrfs_delayed_ref_head *
 btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr)
 {
-	struct btrfs_delayed_ref_node *ref;
 	struct btrfs_delayed_ref_root *delayed_refs;
 
 	delayed_refs = &trans->transaction->delayed_refs;
-	ref = find_ref_head(&delayed_refs->root, bytenr, NULL, 0);
-	if (ref)
-		return btrfs_delayed_node_to_head(ref);
-	return NULL;
+	return find_ref_head(&delayed_refs->href_root, bytenr, NULL, 0);
 }
 
 void btrfs_delayed_ref_exit(void)