xfs: don't commit the first deferred transaction without intents

If the first operation in a string of defer ops has no intents,
then there is no reason to commit it before running the first call
to xfs_defer_finish_one(). This allows the defer ops to be used
effectively for non-intent based operations without requiring an
unnecessary extra transaction commit when first called.

This fixes a regression in per-attribute modification transaction
count when delayed attributes are not being used.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_defer.c

@@ -186,7 +186,7 @@ static const struct xfs_defer_op_type *defer_op_types[] = {
 	[XFS_DEFER_OPS_TYPE_AGFL_FREE]	= &xfs_agfl_free_defer_type,
 };
 
-static void
+static bool
 xfs_defer_create_intent(
 	struct xfs_trans		*tp,
 	struct xfs_defer_pending	*dfp,
@@ -197,6 +197,7 @@ xfs_defer_create_intent(
 	if (!dfp->dfp_intent)
 		dfp->dfp_intent = ops->create_intent(tp, &dfp->dfp_work,
 						     dfp->dfp_count, sort);
+	return dfp->dfp_intent != NULL;
 }
 
 /*
@@ -204,16 +205,18 @@ xfs_defer_create_intent(
  * associated extents, then add the entire intake list to the end of
  * the pending list.
  */
-STATIC void
+static bool
 xfs_defer_create_intents(
 	struct xfs_trans		*tp)
 {
 	struct xfs_defer_pending	*dfp;
+	bool				ret = false;
 
 	list_for_each_entry(dfp, &tp->t_dfops, dfp_list) {
 		trace_xfs_defer_create_intent(tp->t_mountp, dfp);
-		xfs_defer_create_intent(tp, dfp, true);
+		ret |= xfs_defer_create_intent(tp, dfp, true);
 	}
+	return ret;
 }
 
 /* Abort all the intents that were committed. */
@@ -487,7 +490,7 @@ int
 xfs_defer_finish_noroll(
 	struct xfs_trans		**tp)
 {
-	struct xfs_defer_pending	*dfp;
+	struct xfs_defer_pending	*dfp = NULL;
 	int				error = 0;
 	LIST_HEAD(dop_pending);
 
@@ -506,17 +509,20 @@ xfs_defer_finish_noroll(
 		 * of time that any one intent item can stick around in memory,
 		 * pinning the log tail.
 		 */
-		xfs_defer_create_intents(*tp);
+		bool has_intents = xfs_defer_create_intents(*tp);
+
 		list_splice_init(&(*tp)->t_dfops, &dop_pending);
 
-		error = xfs_defer_trans_roll(tp);
-		if (error)
-			goto out_shutdown;
+		if (has_intents || dfp) {
+			error = xfs_defer_trans_roll(tp);
+			if (error)
+				goto out_shutdown;
 
-		/* Possibly relog intent items to keep the log moving. */
-		error = xfs_defer_relog(tp, &dop_pending);
-		if (error)
-			goto out_shutdown;
+			/* Relog intent items to keep the log moving. */
+			error = xfs_defer_relog(tp, &dop_pending);
+			if (error)
+				goto out_shutdown;
+		}
 
 		dfp = list_first_entry(&dop_pending, struct xfs_defer_pending,
 				       dfp_list);