xfs: Don't wake xfsbufd when idle

The xfsbufd wakes every xfsbufd_centisecs (once per second by
default) for each filesystem even when the filesystem is idle.  If
the xfsbufd has nothing to do, put it into a long term sleep and
only wake it up when there is work pending (i.e. dirty buffers to
flush soon). This will make laptop power misers happy.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index 77b8be81c769..18ae3ba8f78a 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -1595,6 +1595,11 @@ xfs_buf_delwri_queue(
                 list_del(&bp->b_list);
         }
 
+        if (list_empty(dwq)) {
+                /* start xfsbufd as it is about to have something to do */
+                wake_up_process(bp->b_target->bt_task);
+        }
+
         bp->b_flags |= _XBF_DELWRI_Q;
         list_add_tail(&bp->b_list, dwq);
         bp->b_queuetime = jiffies;
@@ -1644,6 +1649,8 @@ xfsbufd_wakeup(
         list_for_each_entry(btp, &xfs_buftarg_list, bt_list) {
                 if (test_bit(XBT_FORCE_SLEEP, &btp->bt_flags))
                         continue;
+                if (list_empty(&btp->bt_delwrite_queue))
+                        continue;
                 set_bit(XBT_FORCE_FLUSH, &btp->bt_flags);
                 wake_up_process(btp->bt_task);
         }
@@ -1708,6 +1715,9 @@ xfsbufd(
         set_freezable();
 
         do {
+                long    age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
+                long    tout = xfs_buf_timer_centisecs * msecs_to_jiffies(10);
+
                 if (unlikely(freezing(current))) {
                         set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                         refrigerator();
@@ -1715,12 +1725,12 @@ xfsbufd(
                         clear_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                 }
 
-                schedule_timeout_interruptible(
-                        xfs_buf_timer_centisecs * msecs_to_jiffies(10));
-
-                xfs_buf_delwri_split(target, &tmp,
-                                xfs_buf_age_centisecs * msecs_to_jiffies(10));
+                /* sleep for a long time if there is nothing to do. */
+                if (list_empty(&target->bt_delwrite_queue))
+                        tout = MAX_SCHEDULE_TIMEOUT;
+                schedule_timeout_interruptible(tout);
 
+                xfs_buf_delwri_split(target, &tmp, age);
                 count = 0;
                 while (!list_empty(&tmp)) {
                         bp = list_entry(tmp.next, xfs_buf_t, b_list);