Btrfs: cache extent state when writing out dirty metadata pages

Everytime we write out dirty pages we search for an offset in the tree,
convert the bits in the state, and then when we wait we search for the
offset again and clear the bits.  So for every dirty range in the io tree we
are doing 4 rb searches, which is suboptimal.  With this patch we are only
doing 2 searches for every cycle (modulo weird things happening).  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/extent-tree.c

@@ -312,7 +312,8 @@ static u64 add_new_free_space(struct btrfs_block_group_cache *block_group,
 	while (start < end) {
 		ret = find_first_extent_bit(info->pinned_extents, start,
 					    &extent_start, &extent_end,
-					    EXTENT_DIRTY | EXTENT_UPTODATE);
+					    EXTENT_DIRTY | EXTENT_UPTODATE,
+					    NULL);
 		if (ret)
 			break;
 
@@ -5045,7 +5046,7 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
 
 	while (1) {
 		ret = find_first_extent_bit(unpin, 0, &start, &end,
-					    EXTENT_DIRTY);
+					    EXTENT_DIRTY, NULL);
 		if (ret)
 			break;