btrfs: track refs in a rb_tree instead of a list

If we get a significant amount of delayed refs for a single block (think
modifying multiple snapshots) we can end up spending an ungodly amount
of time looping through all of the entries trying to see if they can be
merged.  This is because we only add them to a list, so we have O(2n)
for every ref head.  This doesn't make any sense as we likely have refs
for different roots, and so they cannot be merged.  Tracking in a tree
will allow us to break as soon as we hit an entry that doesn't match,
making our worst case O(n).

With this we can also merge entries more easily.  Before we had to hope
that matching refs were on the ends of our list, but with the tree we
can search down to exact matches and merge them at insert time.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index fc9720e28005..673ac4e01dd0 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2519,7 +2519,7 @@ select_delayed_ref(struct btrfs_delayed_ref_head *head)
 {
 	struct btrfs_delayed_ref_node *ref;
 
-	if (list_empty(&head->ref_list))
+	if (RB_EMPTY_ROOT(&head->ref_tree))
 		return NULL;
 
 	/*
@@ -2532,8 +2532,8 @@ select_delayed_ref(struct btrfs_delayed_ref_head *head)
 		return list_first_entry(&head->ref_add_list,
 				struct btrfs_delayed_ref_node, add_list);
 
-	ref = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node,
-			       list);
+	ref = rb_entry(rb_first(&head->ref_tree),
+		       struct btrfs_delayed_ref_node, ref_node);
 	ASSERT(list_empty(&ref->add_list));
 	return ref;
 }
@@ -2593,7 +2593,7 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
 	spin_unlock(&head->lock);
 	spin_lock(&delayed_refs->lock);
 	spin_lock(&head->lock);
-	if (!list_empty(&head->ref_list) || head->extent_op) {
+	if (!RB_EMPTY_ROOT(&head->ref_tree) || head->extent_op) {
 		spin_unlock(&head->lock);
 		spin_unlock(&delayed_refs->lock);
 		return 1;
@@ -2740,7 +2740,8 @@ static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 
 		actual_count++;
 		ref->in_tree = 0;
-		list_del(&ref->list);
+		rb_erase(&ref->ref_node, &locked_ref->ref_tree);
+		RB_CLEAR_NODE(&ref->ref_node);
 		if (!list_empty(&ref->add_list))
 			list_del(&ref->add_list);
 		/*
@@ -3138,6 +3139,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
 	struct btrfs_delayed_data_ref *data_ref;
 	struct btrfs_delayed_ref_root *delayed_refs;
 	struct btrfs_transaction *cur_trans;
+	struct rb_node *node;
 	int ret = 0;
 
 	cur_trans = root->fs_info->running_transaction;
@@ -3170,7 +3172,12 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
 	spin_unlock(&delayed_refs->lock);
 
 	spin_lock(&head->lock);
-	list_for_each_entry(ref, &head->ref_list, list) {
+	/*
+	 * XXX: We should replace this with a proper search function in the
+	 * future.
+	 */
+	for (node = rb_first(&head->ref_tree); node; node = rb_next(node)) {
+		ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
 		/* If it's a shared ref we know a cross reference exists */
 		if (ref->type != BTRFS_EXTENT_DATA_REF_KEY) {
 			ret = 1;
@@ -7141,7 +7148,7 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
 		goto out_delayed_unlock;
 
 	spin_lock(&head->lock);
-	if (!list_empty(&head->ref_list))
+	if (!RB_EMPTY_ROOT(&head->ref_tree))
 		goto out;
 
 	if (head->extent_op) {