Btrfs: optimize the error handle of use_block_rsv()

cc: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>

fs/btrfs/extent-tree.c

@@ -6656,28 +6656,16 @@ use_block_rsv(struct btrfs_trans_handle *trans,
 
 	block_rsv = get_block_rsv(trans, root);
 
-	if (block_rsv->size == 0) {
-		ret = reserve_metadata_bytes(root, block_rsv, blocksize,
-					     BTRFS_RESERVE_NO_FLUSH);
-		/*
-		 * If we couldn't reserve metadata bytes try and use some from
-		 * the global reserve.
-		 */
-		if (ret && block_rsv != global_rsv) {
-			ret = block_rsv_use_bytes(global_rsv, blocksize);
-			if (!ret)
-				return global_rsv;
-			return ERR_PTR(ret);
-		} else if (ret) {
-			return ERR_PTR(ret);
-		}
-		return block_rsv;
-	}
+	if (unlikely(block_rsv->size == 0))
+		goto try_reserve;
 
 	ret = block_rsv_use_bytes(block_rsv, blocksize);
 	if (!ret)
 		return block_rsv;
-	if (ret && !block_rsv->failfast) {
+
+	if (block_rsv->failfast)
+		return ERR_PTR(ret);
+
 	if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
 		static DEFINE_RATELIMIT_STATE(_rs,
 				DEFAULT_RATELIMIT_INTERVAL * 10,
@@ -6686,18 +6674,21 @@ use_block_rsv(struct btrfs_trans_handle *trans,
 			WARN(1, KERN_DEBUG
 				"btrfs: block rsv returned %d\n", ret);
 	}
+try_reserve:
 	ret = reserve_metadata_bytes(root, block_rsv, blocksize,
 				     BTRFS_RESERVE_NO_FLUSH);
-		if (!ret) {
+	if (!ret)
 		return block_rsv;
-		} else if (ret && block_rsv != global_rsv) {
+	/*
+	 * If we couldn't reserve metadata bytes try and use some from
+	 * the global reserve.
+	 */
+	if (block_rsv->type != BTRFS_BLOCK_RSV_GLOBAL) {
 		ret = block_rsv_use_bytes(global_rsv, blocksize);
 		if (!ret)
 			return global_rsv;
 	}
-	}
-
-	return ERR_PTR(-ENOSPC);
+	return ERR_PTR(ret);
 }
 
 static void unuse_block_rsv(struct btrfs_fs_info *fs_info,