[PATCH] bdi: use deferable timer for sync_supers task

[Yong Wang]

sync_supers task currently wakes up periodically for superblock
writeback. This hurts power on battery driven devices. This patch
turns this housekeeping timer into a deferable timer so that it
does not fire when system is really idle.

Signed-off-by: Yong Wang <yong.y.wang@xxxxxxxxx>
Signed-off-by: Xia Wu <xia.wu@xxxxxxxxx>
---
 mm/backing-dev.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 65d4204..9a8daa5 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -238,7 +238,9 @@ static int __init default_bdi_init(void)
 	sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
 	BUG_ON(IS_ERR(sync_supers_tsk));
 
-	setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
+	init_timer_deferrable(&sync_supers_timer);
+	sync_supers_timer.function = sync_supers_timer_fn;
+	sync_supers_timer.data = 0;
 	bdi_arm_supers_timer();
 
 	err = bdi_init(&default_backing_dev_info);
-- 
1.5.5.1

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