[PATCH 0/2] Backref iterator size reduction

[PATCH 0/2] Backref iterator size reduction

[David Sterba]

Remove fs_info from struct btrfs_backref_iter and replace allocation by
on-stack usage.

David Sterba (2):
  btrfs: remove fs_info from struct btrfs_backref_iter
  btrfs: use on stack backref iterator in build_backref_tree()

 fs/btrfs/backref.c    | 39 ++++++++++++++-------------------------
 fs/btrfs/backref.h    |  9 ++++-----
 fs/btrfs/relocation.c | 13 ++++++-------
 3 files changed, 24 insertions(+), 37 deletions(-)

-- 
2.53.0

[PATCH 1/2] btrfs: remove fs_info from struct btrfs_backref_iter

[David Sterba]

The fs_info is available everywhere and we don't need to store it inside
a structure that is used within one function only, which is
build_backref_tree(). The size of btrfs_backref_iter is now 48 bytes.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/backref.c    | 19 ++++++++-----------
 fs/btrfs/backref.h    |  7 +++----
 fs/btrfs/relocation.c |  2 +-
 3 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 2c25e5d86f3e42..303f6cfc97c10d 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -2814,7 +2814,7 @@ struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
 	return ifp;
 }
 
-struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info)
+struct btrfs_backref_iter *btrfs_backref_iter_alloc(void)
 {
 	struct btrfs_backref_iter *ret;
 
@@ -2831,7 +2831,6 @@ struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_inf
 	/* Current backref iterator only supports iteration in commit root */
 	ret->path->search_commit_root = true;
 	ret->path->skip_locking = true;
-	ret->fs_info = fs_info;
 
 	return ret;
 }
@@ -2846,9 +2845,8 @@ static void btrfs_backref_iter_release(struct btrfs_backref_iter *iter)
 	memset(&iter->cur_key, 0, sizeof(iter->cur_key));
 }
 
-int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr)
+int btrfs_backref_iter_start(struct btrfs_fs_info *fs_info, struct btrfs_backref_iter *iter, u64 bytenr)
 {
-	struct btrfs_fs_info *fs_info = iter->fs_info;
 	struct btrfs_root *extent_root = btrfs_extent_root(fs_info, bytenr);
 	struct btrfs_path *path = iter->path;
 	struct btrfs_extent_item *ei;
@@ -2963,7 +2961,7 @@ static bool btrfs_backref_iter_is_inline_ref(struct btrfs_backref_iter *iter)
  * Return >0 if there is no extra backref for this bytenr.
  * Return <0 if there is something wrong happened.
  */
-int btrfs_backref_iter_next(struct btrfs_backref_iter *iter)
+int btrfs_backref_iter_next(struct btrfs_fs_info *fs_info, struct btrfs_backref_iter *iter)
 {
 	struct extent_buffer *eb = iter->path->nodes[0];
 	struct btrfs_root *extent_root;
@@ -2997,10 +2995,9 @@ int btrfs_backref_iter_next(struct btrfs_backref_iter *iter)
 	}
 
 	/* We're at keyed items, there is no inline item, go to the next one */
-	extent_root = btrfs_extent_root(iter->fs_info, iter->bytenr);
+	extent_root = btrfs_extent_root(fs_info, iter->bytenr);
 	if (unlikely(!extent_root)) {
-		btrfs_err(iter->fs_info,
-			  "missing extent root for extent at bytenr %llu",
+		btrfs_err(fs_info, "missing extent root for extent at bytenr %llu",
 			  iter->bytenr);
 		return -EUCLEAN;
 	}
@@ -3454,7 +3451,7 @@ int btrfs_backref_add_tree_node(struct btrfs_trans_handle *trans,
 	struct btrfs_backref_node *exist;
 	int ret;
 
-	ret = btrfs_backref_iter_start(iter, cur->bytenr);
+	ret = btrfs_backref_iter_start(trans->fs_info, iter, cur->bytenr);
 	if (ret < 0)
 		return ret;
 	/*
@@ -3462,7 +3459,7 @@ int btrfs_backref_add_tree_node(struct btrfs_trans_handle *trans,
 	 * stored in it, but fetch it from the tree block
 	 */
 	if (btrfs_backref_has_tree_block_info(iter)) {
-		ret = btrfs_backref_iter_next(iter);
+		ret = btrfs_backref_iter_next(trans->fs_info, iter);
 		if (ret < 0)
 			goto out;
 		/* No extra backref? This means the tree block is corrupted */
@@ -3492,7 +3489,7 @@ int btrfs_backref_add_tree_node(struct btrfs_trans_handle *trans,
 		exist = NULL;
 	}
 
-	for (; ret == 0; ret = btrfs_backref_iter_next(iter)) {
+	for (; ret == 0; ret = btrfs_backref_iter_next(trans->fs_info, iter)) {
 		struct extent_buffer *eb;
 		struct btrfs_key key;
 		int type;
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index 1d009b0f4c699a..96717460e2e04d 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -278,14 +278,13 @@ struct prelim_ref {
 struct btrfs_backref_iter {
 	u64 bytenr;
 	struct btrfs_path *path;
-	struct btrfs_fs_info *fs_info;
 	struct btrfs_key cur_key;
 	u32 item_ptr;
 	u32 cur_ptr;
 	u32 end_ptr;
 };
 
-struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info);
+struct btrfs_backref_iter *btrfs_backref_iter_alloc(void);
 
 /*
  * For metadata with EXTENT_ITEM key (non-skinny) case, the first inline data
@@ -302,9 +301,9 @@ static inline bool btrfs_backref_has_tree_block_info(
 	return false;
 }
 
-int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr);
+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_backref_iter *iter);
+int btrfs_backref_iter_next(struct btrfs_fs_info *fs_info, struct btrfs_backref_iter *iter);
 
 /*
  * Backref cache related structures
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 9cbae3cf8bdd1e..843fdcacb31555 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -416,7 +416,7 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 	struct btrfs_backref_edge *edge;
 	int ret;
 
-	iter = btrfs_backref_iter_alloc(rc->extent_root->fs_info);
+	iter = btrfs_backref_iter_alloc();
 	if (!iter)
 		return ERR_PTR(-ENOMEM);
 	path = btrfs_alloc_path();
-- 
2.53.0

[PATCH 2/2] btrfs: use on stack backref iterator in build_backref_tree()

[David Sterba]

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>
---
 fs/btrfs/backref.c    | 22 +++++++---------------
 fs/btrfs/backref.h    |  4 ++--
 fs/btrfs/relocation.c | 13 ++++++-------
 3 files changed, 15 insertions(+), 24 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 303f6cfc97c10d..0abcec0ceead0c 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 96717460e2e04d..179791de6b1955 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 843fdcacb31555..67af02e732d0ce 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);
-- 
2.53.0