Btrfs: Optimize tree log block allocations

Since tree log blocks get freed every transaction, they never really
need to be written to disk.  This skips the step where we update
metadata to record they were allocated.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index f43ee33..5f77bee 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1728,9 +1728,8 @@
 
 				WARN_ON(root_owner !=
 					BTRFS_TREE_LOG_OBJECTID);
-				ret = btrfs_free_extent(trans, root, bytenr,
-							blocksize, root_owner,
-							root_gen, 0, 0, 1);
+				ret = btrfs_free_reserved_extent(root,
+							 bytenr, blocksize);
 				BUG_ON(ret);
 			}
 			free_extent_buffer(next);
@@ -1775,8 +1774,7 @@
 			BUG_ON(ret);
 		}
 		WARN_ON(root_owner != BTRFS_TREE_LOG_OBJECTID);
-		ret = btrfs_free_extent(trans, root, bytenr, blocksize,
-					  root_owner, root_gen, 0, 0, 1);
+		ret = btrfs_free_reserved_extent(root, bytenr, blocksize);
 		BUG_ON(ret);
 	}
 	free_extent_buffer(path->nodes[*level]);
@@ -1837,10 +1835,9 @@
 				}
 
 				WARN_ON(root_owner != BTRFS_TREE_LOG_OBJECTID);
-				ret = btrfs_free_extent(trans, root,
+				ret = btrfs_free_reserved_extent(root,
 						path->nodes[*level]->start,
-						path->nodes[*level]->len,
-						root_owner, root_gen, 0, 0, 1);
+						path->nodes[*level]->len);
 				BUG_ON(ret);
 			}
 			free_extent_buffer(path->nodes[*level]);
@@ -1910,11 +1907,8 @@
 			}
 			WARN_ON(log->root_key.objectid !=
 				BTRFS_TREE_LOG_OBJECTID);
-			ret = btrfs_free_extent(trans, log,
-						next->start, next->len,
-						log->root_key.objectid,
-						btrfs_header_generation(next),
-						0, 0, 1);
+			ret = btrfs_free_reserved_extent(log, next->start,
+							 next->len);
 			BUG_ON(ret);
 		}
 	}