[patch] Prevent excessive xfsaild wakeups

[David Chinner <dgc@sgi.com>]

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 will result repeated looping to push everything past
the target when everything because it fails to check if we
managed to push anything.

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

Signed-off-by: Dave Chinner <dgc@sgi.com>
---
 fs/xfs/xfs_trans_ail.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

Index: 2.6.x-xfs-new/fs/xfs/xfs_trans_ail.c
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/xfs_trans_ail.c	2008-02-18 09:14:34.000000000 +1100
+++ 2.6.x-xfs-new/fs/xfs/xfs_trans_ail.c	2008-02-18 09:18:52.070682570 +1100
@@ -261,14 +261,17 @@ 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 && (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 (!count) {
+		/* We're past our target or empty, so idle */
+		tout = 1000;
 	} else if ((restarts > XFS_TRANS_PUSH_AIL_RESTARTS) ||
 		   (count && ((stuck * 100) / count > 90))) {
 		/*