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>

3 files changed, 23 insertions, 21 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7c06eb4ecfdd..5edb7f885799 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -829,9 +829,8 @@ int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
 	WARN_ON(btrfs_header_level(eb) != 0);
 	WARN_ON(btrfs_header_nritems(eb) != 0);
 
-	ret = btrfs_free_extent(trans, fs_info->tree_root,
-				eb->start, eb->len,
-				BTRFS_TREE_LOG_OBJECTID, 0, 0, 0, 1);
+	ret = btrfs_free_reserved_extent(fs_info->tree_root,
+				eb->start, eb->len);
 	BUG_ON(ret);
 
 	free_extent_buffer(eb);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3181759da1cf..c479d71e2869 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1872,8 +1872,15 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 		return 0;
 	}
 	/* if metadata always pin */
-	if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID)
+	if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID) {
+		if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
+			/* btrfs_free_reserved_extent */
+			set_extent_dirty(&root->fs_info->free_space_cache,
+				 bytenr, bytenr + num_bytes - 1, GFP_NOFS);
+			return 0;
+		}
 		pin = 1;
+	}
 
 	/* if data pin when any transaction has committed this */
 	if (ref_generation != trans->transid)
@@ -2361,11 +2368,13 @@ int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 				     min_alloc_size, empty_size, hint_byte,
 				     search_end, ins, data);
 	BUG_ON(ret);
-	ret = __btrfs_alloc_reserved_extent(trans, root, root_objectid,
-					    ref_generation, owner,
-					    owner_offset, ins);
-	BUG_ON(ret);
+	if (root_objectid != BTRFS_TREE_LOG_OBJECTID) {
+		ret = __btrfs_alloc_reserved_extent(trans, root, root_objectid,
+						    ref_generation, owner,
+						    owner_offset, ins);
+		BUG_ON(ret);
 
+	}
 	maybe_unlock_mutex(root);
 	return ret;
 }
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index f43ee33ec2dc..5f77bee0f846 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -1728,9 +1728,8 @@ static int noinline walk_down_log_tree(struct btrfs_trans_handle *trans,
 
 				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 @@ static int noinline walk_down_log_tree(struct btrfs_trans_handle *trans,
 			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 @@ static int noinline walk_up_log_tree(struct btrfs_trans_handle *trans,
 				}
 
 				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 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
 			}
 			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);
 		}
 	}