[XFS] 977545 977545 977545 977545 977545 977545 xfsaild causing too many

wakeups

Idle state is not being detected properly by the xfsaild push code. The
current idle state is detected by an empty list which may never happen
with mostly idle filesystem or one using lazy superblock counters. A
single dirty item in the list that exists beyond the push target can
result repeated looping attempting to push up to the target because it
fails to check if the push target has been acheived or not.

Fix by considering a dirty list with everything past the target as an idle
state and set the timeout appropriately.

SGI-PV: 977545
SGI-Modid: xfs-linux-melb:xfs-kern:30532a
Signed-off-by: NDavid Chinner <dgc@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NLachlan McIlroy <lachlan@sgi.com>

fs/xfs/xfs_trans_ail.c

@@ -261,16 +261,19 @@ xfsaild_push(
 		xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
 	}
 
-	/*
-	 * We reached the target so wait a bit longer for I/O to complete and
-	 * remove pushed items from the AIL before we start the next scan from
-	 * the start of the AIL.
-	 */
-	if ((XFS_LSN_CMP(lsn, target) >= 0)) {
+	if (!count) {
+		/* We're past our target or empty, so idle */
+		tout = 1000;
+	} else if (XFS_LSN_CMP(lsn, target) >= 0) {
+		/*
+		 * We reached the target so wait a bit longer for I/O to
+		 * complete and remove pushed items from the AIL before we
+		 * start the next scan from the start of the AIL.
+		 */
 		tout += 20;
 		last_pushed_lsn = 0;
 	} else if ((restarts > XFS_TRANS_PUSH_AIL_RESTARTS) ||
-		   (count && ((stuck * 100) / count > 90))) {
+		   ((stuck * 100) / count > 90)) {
 		/*
 		 * Either there is a lot of contention on the AIL or we
 		 * are stuck due to operations in progress. "Stuck" in this