---

yaml
---
r: 274360
b: refs/heads/master
c: c8462cc
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 143dfe8611a63030ce0c79419dc362f7838be557
+refs/heads/master: c8462cc9de9e92264ec647903772f6036a99b286

trunk/mm/page-writeback.c

@@ -939,6 +939,43 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
 	return 1;
 }
 
+static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
+				   unsigned long bdi_dirty)
+{
+	unsigned long bw = bdi->avg_write_bandwidth;
+	unsigned long hi = ilog2(bw);
+	unsigned long lo = ilog2(bdi->dirty_ratelimit);
+	unsigned long t;
+
+	/* target for 20ms max pause on 1-dd case */
+	t = HZ / 50;
+
+	/*
+	 * Scale up pause time for concurrent dirtiers in order to reduce CPU
+	 * overheads.
+	 *
+	 * (N * 20ms) on 2^N concurrent tasks.
+	 */
+	if (hi > lo)
+		t += (hi - lo) * (20 * HZ) / 1024;
+
+	/*
+	 * Limit pause time for small memory systems. If sleeping for too long
+	 * time, a small pool of dirty/writeback pages may go empty and disk go
+	 * idle.
+	 *
+	 * 8 serves as the safety ratio.
+	 */
+	if (bdi_dirty)
+		t = min(t, bdi_dirty * HZ / (8 * bw + 1));
+
+	/*
+	 * The pause time will be settled within range (max_pause/4, max_pause).
+	 * Apply a minimal value of 4 to get a non-zero max_pause/4.
+	 */
+	return clamp_val(t, 4, MAX_PAUSE);
+}
+
 /*
  * balance_dirty_pages() must be called by processes which are generating dirty
  * data.  It looks at the number of dirty pages in the machine and will force
@@ -958,6 +995,7 @@ static void balance_dirty_pages(struct address_space *mapping,
 	unsigned long dirty_thresh;
 	unsigned long bdi_thresh;
 	long pause = 0;
+	long max_pause;
 	bool dirty_exceeded = false;
 	unsigned long task_ratelimit;
 	unsigned long dirty_ratelimit;
@@ -1035,18 +1073,20 @@ static void balance_dirty_pages(struct address_space *mapping,
 				     nr_dirty, bdi_thresh, bdi_dirty,
 				     start_time);
 
+		max_pause = bdi_max_pause(bdi, bdi_dirty);
+
 		dirty_ratelimit = bdi->dirty_ratelimit;
 		pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
 					       background_thresh, nr_dirty,
 					       bdi_thresh, bdi_dirty);
 		if (unlikely(pos_ratio == 0)) {
-			pause = MAX_PAUSE;
+			pause = max_pause;
 			goto pause;
 		}
 		task_ratelimit = (u64)dirty_ratelimit *
 					pos_ratio >> RATELIMIT_CALC_SHIFT;
 		pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
-		pause = min_t(long, pause, MAX_PAUSE);
+		pause = min(pause, max_pause);
 
 pause:
 		__set_current_state(TASK_UNINTERRUPTIBLE);