writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()

global_update_bandwidth() uses static variable update_time as the
timestamp for the last update but forgets to initialize it to
INITIALIZE_JIFFIES.

This means that global_dirty_limit will be 5 mins into the future on
32bit and some large amount jiffies into the past on 64bit.  This
isn't critical as the only effect is that global_dirty_limit won't be
updated for the first 5 mins after booting on 32bit machines,
especially given the auxiliary nature of global_dirty_limit's role -
protecting against global dirty threshold's sudden dips; however, it
does lead to unintended suboptimal behavior.  Fix it.

Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 45e187b2d971..b4fd980a93eb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -922,7 +922,7 @@ static void global_update_bandwidth(unsigned long thresh,
                                     unsigned long now)
 {
         static DEFINE_SPINLOCK(dirty_lock);
-        static unsigned long update_time;
+        static unsigned long update_time = INITIAL_JIFFIES;
 
         /*
          * check locklessly first to optimize away locking for the most time