btrfs: use on stack backref iterator in build_backref_tree()

The iterator is used only once and within build_backref_tree() so we can
avoid one allocation and place it on stack.

Signed-off-by: David Sterba <dsterba@suse.com>

3 files changed, 15 insertions, 24 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 303f6cfc97c1..0abcec0ceead 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -2814,25 +2814,17 @@ struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
 	return ifp;
 }
 
-struct btrfs_backref_iter *btrfs_backref_iter_alloc(void)
+int btrfs_backref_iter_init(struct btrfs_backref_iter *iter)
 {
-	struct btrfs_backref_iter *ret;
-
-	ret = kzalloc_obj(*ret, GFP_NOFS);
-	if (!ret)
-		return NULL;
-
-	ret->path = btrfs_alloc_path();
-	if (!ret->path) {
-		kfree(ret);
-		return NULL;
-	}
+	iter->path = btrfs_alloc_path();
+	if (!iter->path)
+		return -ENOMEM;
 
 	/* Current backref iterator only supports iteration in commit root */
-	ret->path->search_commit_root = true;
-	ret->path->skip_locking = true;
+	iter->path->search_commit_root = true;
+	iter->path->skip_locking = true;
 
-	return ret;
+	return 0;
 }
 
 static void btrfs_backref_iter_release(struct btrfs_backref_iter *iter)
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index 96717460e2e0..179791de6b19 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -284,8 +284,6 @@ struct btrfs_backref_iter {
 	u32 end_ptr;
 };
 
-struct btrfs_backref_iter *btrfs_backref_iter_alloc(void);
-
 /*
  * For metadata with EXTENT_ITEM key (non-skinny) case, the first inline data
  * is btrfs_tree_block_info, without a btrfs_extent_inline_ref header.
@@ -301,6 +299,8 @@ static inline bool btrfs_backref_has_tree_block_info(
 	return false;
 }
 
+int btrfs_backref_iter_init(struct btrfs_backref_iter *iter);
+
 int btrfs_backref_iter_start(struct btrfs_fs_info *fs_info, struct btrfs_backref_iter *iter, u64 bytenr);
 
 int btrfs_backref_iter_next(struct btrfs_fs_info *fs_info, struct btrfs_backref_iter *iter);
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 843fdcacb315..67af02e732d0 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -407,7 +407,7 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 			struct reloc_control *rc, struct btrfs_key *node_key,
 			int level, u64 bytenr)
 {
-	struct btrfs_backref_iter *iter;
+	struct btrfs_backref_iter iter;
 	struct btrfs_backref_cache *cache = &rc->backref_cache;
 	/* For searching parent of TREE_BLOCK_REF */
 	struct btrfs_path *path;
@@ -416,9 +416,9 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 	struct btrfs_backref_edge *edge;
 	int ret;
 
-	iter = btrfs_backref_iter_alloc();
-	if (!iter)
-		return ERR_PTR(-ENOMEM);
+	ret = btrfs_backref_iter_init(&iter);
+	if (ret < 0)
+		return ERR_PTR(ret);
 	path = btrfs_alloc_path();
 	if (!path) {
 		ret = -ENOMEM;
@@ -435,7 +435,7 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 
 	/* Breadth-first search to build backref cache */
 	do {
-		ret = btrfs_backref_add_tree_node(trans, cache, path, iter,
+		ret = btrfs_backref_add_tree_node(trans, cache, path, &iter,
 						  node_key, cur);
 		if (ret < 0)
 			goto out;
@@ -460,8 +460,7 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 	if (handle_useless_nodes(rc, node))
 		node = NULL;
 out:
-	btrfs_free_path(iter->path);
-	kfree(iter);
+	btrfs_free_path(iter.path);
 	btrfs_free_path(path);
 	if (ret) {
 		btrfs_backref_error_cleanup(cache, node);