xfs: only relog deferred intent items if free space in the log gets low

Now that we have the ability to ask the log how far the tail needs to be
pushed to maintain its free space targets, augment the decision to relog
an intent item so that we only do it if the log has hit the 75% full
threshold.  There's no point in relogging an intent into the same
checkpoint, and there's no need to relog if there's plenty of free space
in the log.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/libxfs/xfs_defer.c

@@ -356,7 +356,10 @@ xfs_defer_relog(
 	struct xfs_trans		**tpp,
 	struct list_head		*dfops)
 {
+	struct xlog			*log = (*tpp)->t_mountp->m_log;
 	struct xfs_defer_pending	*dfp;
+	xfs_lsn_t			threshold_lsn = NULLCOMMITLSN;
+
 
 	ASSERT((*tpp)->t_flags & XFS_TRANS_PERM_LOG_RES);
 
@@ -372,6 +375,19 @@ xfs_defer_relog(
 		    xfs_log_item_in_current_chkpt(dfp->dfp_intent))
 			continue;
 
+		/*
+		 * Figure out where we need the tail to be in order to maintain
+		 * the minimum required free space in the log.  Only sample
+		 * the log threshold once per call.
+		 */
+		if (threshold_lsn == NULLCOMMITLSN) {
+			threshold_lsn = xlog_grant_push_threshold(log, 0);
+			if (threshold_lsn == NULLCOMMITLSN)
+				break;
+		}
+		if (XFS_LSN_CMP(dfp->dfp_intent->li_lsn, threshold_lsn) >= 0)
+			continue;
+
 		trace_xfs_defer_relog_intent((*tpp)->t_mountp, dfp);
 		XFS_STATS_INC((*tpp)->t_mountp, defer_relog);
 		dfp->dfp_intent = xfs_trans_item_relog(dfp->dfp_intent, *tpp);