Btrfs: avoid starting a transaction in the write path
I noticed while looking at a deadlock that we are always starting a transaction
in cow_file_range(). This isn't really needed since we only need a transaction
if we are doing an inline extent, or if the allocator needs to allocate a chunk.
So push down all the transaction start stuff to be closer to where we actually
need a transaction in all of these cases. This will hopefully reduce our write
latency when we are committing often. Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8cc941e..5e7ea99 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1339,7 +1339,6 @@
static noinline int check_can_nocow(struct inode *inode, loff_t pos,
size_t *write_bytes)
{
- struct btrfs_trans_handle *trans;
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_ordered_extent *ordered;
u64 lockstart, lockend;
@@ -1361,16 +1360,8 @@
btrfs_put_ordered_extent(ordered);
}
- trans = btrfs_join_transaction(root);
- if (IS_ERR(trans)) {
- unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);
- return PTR_ERR(trans);
- }
-
num_bytes = lockend - lockstart + 1;
- ret = can_nocow_extent(trans, inode, lockstart, &num_bytes, NULL, NULL,
- NULL);
- btrfs_end_transaction(trans, root);
+ ret = can_nocow_extent(inode, lockstart, &num_bytes, NULL, NULL, NULL);
if (ret <= 0) {
ret = 0;
} else {