btrfs: remove FLUSH_DELAYED_REFS from data ENOSPC flushing

Since we unconditionally commit the transaction now we no longer need to
run the delayed refs to make sure our total_bytes_pinned value is
uptodate, we can simply commit the transaction.  Remove this stage from
the data flushing list.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/space-info.c

@@ -1080,21 +1080,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
  *   immediately re-usable, it comes in the form of a delayed ref, which must be
  *   run and then the transaction must be committed.
  *
- * FLUSH_DELAYED_REFS
- *   The above two cases generate delayed refs that will affect
- *   ->total_bytes_pinned.  However this counter can be inconsistent with
- *   reality if there are outstanding delayed refs.  This is because we adjust
- *   the counter based solely on the current set of delayed refs and disregard
- *   any on-disk state which might include more refs.  So for example, if we
- *   have an extent with 2 references, but we only drop 1, we'll see that there
- *   is a negative delayed ref count for the extent and assume that the space
- *   will be freed, and thus increase ->total_bytes_pinned.
- *
- *   Running the delayed refs gives us the actual real view of what will be
- *   freed at the transaction commit time.  This stage will not actually free
- *   space for us, it just makes sure that may_commit_transaction() has all of
- *   the information it needs to make the right decision.
- *
  * COMMIT_TRANS
  *   This is where we reclaim all of the pinned space generated by running the
  *   iputs
@@ -1107,7 +1092,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 static const enum btrfs_flush_state data_flush_states[] = {
 	FLUSH_DELALLOC_WAIT,
 	RUN_DELAYED_IPUTS,
-	FLUSH_DELAYED_REFS,
 	COMMIT_TRANS,
 	ALLOC_CHUNK_FORCE,
 };