Re: [PATCH] Btrfs: kill trans in run_delalloc_nocow and btrfs_cross_ref_exist

[David Sterba]

On Mon, Jan 30, 2017 at 12:25:28PM -0800, Liu Bo wrote:
> run_delalloc_nocow has used trans in two places where they don't actually need
> @trans.
> 
> For btrfs_lookup_file_extent, we search for file extents without COWing
> anything, and for btrfs_cross_ref_exist, the only place where we need @trans 
> is
> deferencing it in order to get running_transaction which we could easily get
> from the global fs_info.
> 
> Signed-off-by: Liu Bo 

Reviewed-by: David Sterba 

Removing the transaction is ok, backed by some patch archeology.
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[PATCH] Btrfs: kill trans in run_delalloc_nocow and btrfs_cross_ref_exist

[Liu Bo]

run_delalloc_nocow has used trans in two places where they don't actually need
@trans.

For btrfs_lookup_file_extent, we search for file extents without COWing
anything, and for btrfs_cross_ref_exist, the only place where we need @trans is
deferencing it in order to get running_transaction which we could easily get
from the global fs_info.

Signed-off-by: Liu Bo 
---
 fs/btrfs/ctree.h   |  3 +--
 fs/btrfs/extent-tree.c | 22 --
 fs/btrfs/inode.c   | 38 +++---
 3 files changed, 16 insertions(+), 47 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 6a82371..73b2d51 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2577,8 +2577,7 @@ int btrfs_pin_extent_for_log_replay(struct btrfs_fs_info 
*fs_info,
u64 bytenr, u64 num_bytes);
 int btrfs_exclude_logged_extents(struct btrfs_fs_info *fs_info,
 struct extent_buffer *eb);
-int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
- struct btrfs_root *root,
+int btrfs_cross_ref_exist(struct btrfs_root *root,
  u64 objectid, u64 offset, u64 bytenr);
 struct btrfs_block_group_cache *btrfs_lookup_block_group(
 struct btrfs_fs_info *info,
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ed254b8..097fa4a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3025,8 +3025,7 @@ int btrfs_set_disk_extent_flags(struct btrfs_trans_handle 
*trans,
return ret;
 }
 
-static noinline int check_delayed_ref(struct btrfs_trans_handle *trans,
- struct btrfs_root *root,
+static noinline int check_delayed_ref(struct btrfs_root *root,
  struct btrfs_path *path,
  u64 objectid, u64 offset, u64 bytenr)
 {
@@ -3034,9 +3033,14 @@ static noinline int check_delayed_ref(struct 
btrfs_trans_handle *trans,
struct btrfs_delayed_ref_node *ref;
struct btrfs_delayed_data_ref *data_ref;
struct btrfs_delayed_ref_root *delayed_refs;
+   struct btrfs_transaction *cur_trans;
int ret = 0;
 
-   delayed_refs = >transaction->delayed_refs;
+   cur_trans = root->fs_info->running_transaction;
+   if (!cur_trans)
+   return 0;
+
+   delayed_refs = _trans->delayed_refs;
spin_lock(_refs->lock);
head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
if (!head) {
@@ -3087,8 +3091,7 @@ static noinline int check_delayed_ref(struct 
btrfs_trans_handle *trans,
return ret;
 }
 
-static noinline int check_committed_ref(struct btrfs_trans_handle *trans,
-   struct btrfs_root *root,
+static noinline int check_committed_ref(struct btrfs_root *root,
struct btrfs_path *path,
u64 objectid, u64 offset, u64 bytenr)
 {
@@ -3159,9 +3162,8 @@ static noinline int check_committed_ref(struct 
btrfs_trans_handle *trans,
return ret;
 }
 
-int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
- struct btrfs_root *root,
- u64 objectid, u64 offset, u64 bytenr)
+int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset,
+ u64 bytenr)
 {
struct btrfs_path *path;
int ret;
@@ -3172,12 +3174,12 @@ int btrfs_cross_ref_exist(struct btrfs_trans_handle 
*trans,
return -ENOENT;
 
do {
-   ret = check_committed_ref(trans, root, path, objectid,
+   ret = check_committed_ref(root, path, objectid,
  offset, bytenr);
if (ret && ret != -ENOENT)
goto out;
 
-   ret2 = check_delayed_ref(trans, root, path, objectid,
+   ret2 = check_delayed_ref(root, path, objectid,
 offset, bytenr);
} while (ret2 == -EAGAIN);
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 082b968..3d3753a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1250,7 +1250,6 @@ static noinline int run_delalloc_nocow(struct inode 
*inode,
 {
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_root *root = BTRFS_I(inode)->root;
-   struct btrfs_trans_handle *trans;
struct extent_buffer *leaf;
struct btrfs_path *path;
struct btrfs_file_extent_item *fi;
@@ -1286,30 +1285,10 @@ static noinline int run_delalloc_nocow(struct inode 
*inode,
 
nolock = btrfs_is_free_space_inode(inode);
 
-   if (nolock)
-   trans = btrfs_join_transaction_nolock(root);
-   else
-   trans = btrfs_join_transaction(root);
-
-   if (IS_ERR(trans)) {
-