writeback: make balance_dirty_pages() gradually back more off

Currently it just sleeps for a very short time, just 1 jiffy. If
we keep looping in there, continually delay for a little longer
of up to 100msec in total. That was the old limit for congestion
wait.

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

1 files changed, 10 insertions, 1 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2585349469e0..d1ba46441053 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -485,6 +485,7 @@ static void balance_dirty_pages(struct address_space *mapping)
         unsigned long bdi_thresh;
         unsigned long pages_written = 0;
         unsigned long write_chunk = sync_writeback_pages();
+        unsigned long pause = 1;
 
         struct backing_dev_info *bdi = mapping->backing_dev_info;
 
@@ -561,7 +562,15 @@ static void balance_dirty_pages(struct address_space *mapping)
                 if (pages_written >= write_chunk)
                         break;          /* We've done our duty */
 
-                schedule_timeout_interruptible(1);
+                schedule_timeout_interruptible(pause);
+
+                /*
+                 * Increase the delay for each loop, up to our previous
+                 * default of taking a 100ms nap.
+                 */
+                pause <<= 1;
+                if (pause > HZ / 10)
+                        pause = HZ / 10;
         }
 
         if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&