[PATCH 24/47] writeback: increase pause time on concurrent dirtiers

[Wu Fengguang]

Increase max pause time to 200ms, and make it work for (HZ < 5).

The larger 200ms will help reduce overheads in server workloads with
lots of concurrent dirtier tasks.

CC: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 mm/page-writeback.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- linux-next.orig/mm/page-writeback.c	2010-12-09 11:52:05.000000000 +0800
+++ linux-next/mm/page-writeback.c	2010-12-09 11:54:05.000000000 +0800
@@ -36,6 +36,11 @@
 #include <linux/pagevec.h>
 #include <trace/events/writeback.h>
 
+/*
+ * Don't sleep more than 200ms at a time in balance_dirty_pages().
+ */
+#define MAX_PAUSE	max(HZ/5, 1)
+
 /* The following parameters are exported via /proc/sys/vm */
 
 /*
@@ -660,7 +665,7 @@ static void balance_dirty_pages(struct a
 		bdi_update_bandwidth(bdi, start_time, bdi_dirty, bdi_thresh);
 
 		if (bdi_dirty >= task_thresh) {
-			pause = HZ/10;
+			pause = MAX_PAUSE;
 			goto pause;
 		}
 
@@ -679,7 +684,7 @@ static void balance_dirty_pages(struct a
 		do_div(bw, bdi_thresh / TASK_SOFT_DIRTY_LIMIT + 1);
 
 		pause = HZ * pages_dirtied / ((unsigned long)bw + 1);
-		pause = clamp_val(pause, 1, HZ/10);
+		pause = clamp_val(pause, 1, MAX_PAUSE);
 
 pause:
 		trace_balance_dirty_pages(bdi,
@@ -714,7 +719,7 @@ pause:
 		current->nr_dirtied_pause = ratelimit_pages(bdi);
 	else if (pause == 1)
 		current->nr_dirtied_pause += current->nr_dirtied_pause / 32 + 1;
-	else if (pause >= HZ/10)
+	else if (pause >= MAX_PAUSE)
 		/*
 		 * when repeated, writing 1 page per 100ms on slow devices,
 		 * i-(i+2)/4 will be able to reach 1 but never reduce to 0.


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