btrfs: avoid unnecessary ref initialization when freeing log tree block

At btrfs_free_tree_block(), we are always initializing a delayed reference
to drop the given extent buffer but we only use if it does not belong to a
log root tree. So we are doing unnecessary work here and increasing the
duration of a critical section as this is normally called while holding a
lock on the parent tree block (if any) and while holding a log transaction
open.

So initialize the delayed reference only if the extent buffer is not from
a log tree, avoiding unnecessary work and making the code also a bit
easier to follow.

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0d72d0f7cefcad224dbc7b251db06b2cc191182e..beedd6ed64d39bd7f53ad814c22df36b80b96235 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3458,16 +3458,17 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
                           u64 parent, int last_ref)
 {
        struct btrfs_fs_info *fs_info = trans->fs_info;
-       struct btrfs_ref generic_ref = { 0 };
        struct btrfs_block_group *bg;
        int ret;
 
-       btrfs_init_generic_ref(&generic_ref, BTRFS_DROP_DELAYED_REF,
-                              buf->start, buf->len, parent, btrfs_header_owner(buf));
-       btrfs_init_tree_ref(&generic_ref, btrfs_header_level(buf),
-                           root_id, 0, false);
-
        if (root_id != BTRFS_TREE_LOG_OBJECTID) {
+               struct btrfs_ref generic_ref = { 0 };
+
+               btrfs_init_generic_ref(&generic_ref, BTRFS_DROP_DELAYED_REF,
+                                      buf->start, buf->len, parent,
+                                      btrfs_header_owner(buf));
+               btrfs_init_tree_ref(&generic_ref, btrfs_header_level(buf),
+                                   root_id, 0, false);
                btrfs_ref_tree_mod(fs_info, &generic_ref);
                ret = btrfs_add_delayed_tree_ref(trans, &generic_ref, NULL);
                BUG_ON(ret); /* -ENOMEM */