writeback: fixups for !dirty_writeback_centisecs

Commit 69b62d01 fixed up most of the places where we would enter
busy schedule() spins when disabling the periodic background
writeback. This fixes up the sb timer so that it doesn't get
hammered on with the delay disabled, and ensures that it gets
rearmed if needed when /proc/sys/vm/dirty_writeback_centisecs
gets modified.

bdi_forker_task() also needs to check for !dirty_writeback_centisecs
and use schedule() appropriately, fix that up too.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 53b2fcf2d283..0d7bbe859550 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -690,6 +690,7 @@ int dirty_writeback_centisecs_handler(ctl_table *table, int write,
         void __user *buffer, size_t *length, loff_t *ppos)
 {
         proc_dointvec(table, write, buffer, length, ppos);
+        bdi_arm_supers_timer();
         return 0;
 }