When there are only one (or several) dirtiers, dirty_exceeded is always
(or mostly) off. Converting to timestamp avoids this problem. It helps
to use smaller write_chunk for smoother throttling.
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
Before patch, the wait time in balance_dirty_pages() are ~200ms:
[ 1093.397700] write_bandwidth: comm=swapper pages=1536 time=204ms
[ 1093.594319] write_bandwidth: comm=swapper pages=1536 time=196ms
[ 1093.796642] write_bandwidth: comm=swapper pages=1536 time=200ms
After patch, ~25ms:
[ 90.261339] write_bandwidth: comm=swapper pages=192 time=20ms
[ 90.293168] write_bandwidth: comm=swapper pages=192 time=24ms
[ 90.323853] write_bandwidth: comm=swapper pages=192 time=24ms
[ 90.354510] write_bandwidth: comm=swapper pages=192 time=28ms
[ 90.389890] write_bandwidth: comm=swapper pages=192 time=28ms
[ 90.421787] write_bandwidth: comm=swapper pages=192 time=24ms
include/linux/backing-dev.h | 2 +-
mm/backing-dev.c | 2 --
mm/page-writeback.c | 24 ++++++++++++------------
3 files changed, 13 insertions(+), 15 deletions(-)
--- linux-next.orig/mm/page-writeback.c 2011-06-19 22:59:49.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-06-19 22:59:53.000000000 +0800
@@ -483,6 +483,15 @@ unsigned long bdi_dirty_limit(struct bac
return bdi_dirty;
}
+/*
+ * last time exceeded (limit - limit/DIRTY_BRAKE)
+ */
+static bool dirty_exceeded_recently(struct backing_dev_info *bdi,
+ unsigned long time_window)
+{
+ return jiffies - bdi->dirty_exceed_time <= time_window;
+}
+
static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
unsigned long elapsed,
unsigned long written)
@@ -621,7 +630,6 @@ static void balance_dirty_pages(struct a
unsigned long bdi_thresh;
unsigned long pages_written = 0;
unsigned long pause = 1;
- bool dirty_exceeded = false;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;
@@ -669,14 +677,9 @@ static void balance_dirty_pages(struct a
* bdi or process from holding back light ones; The latter is
* the last resort safeguard.
*/
- dirty_exceeded = (bdi_dirty > bdi_thresh) ||
- (nr_dirty > dirty_thresh);
-
- if (!dirty_exceeded)
+ if (bdi_dirty <= bdi_thresh && nr_dirty <= dirty_thresh)
break;
-
- if (!bdi->dirty_exceeded)
- bdi->dirty_exceeded = 1;
+ bdi->dirty_exceed_time = jiffies;
bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty, bdi_dirty,
start_time);
@@ -719,9 +722,6 @@ static void balance_dirty_pages(struct a
pause = HZ / 10;
}
- if (!dirty_exceeded && bdi->dirty_exceeded)
- bdi->dirty_exceeded = 0;
-
if (writeback_in_progress(bdi))
return;
@@ -775,7 +775,7 @@ void balance_dirty_pages_ratelimited_nr(
return;
ratelimit = ratelimit_pages;
- if (mapping->backing_dev_info->dirty_exceeded)
+ if (dirty_exceeded_recently(bdi, MAX_PAUSE))
ratelimit = 8;
/*
--- linux-next.orig/include/linux/backing-dev.h 2011-06-19 22:54:58.000000000 +0800
+++ linux-next/include/linux/backing-dev.h 2011-06-19 22:59:53.000000000 +0800
@@ -79,7 +79,7 @@ struct backing_dev_info {
unsigned long avg_write_bandwidth;
struct prop_local_percpu completions;
- int dirty_exceeded;
+ unsigned long dirty_exceed_time;
unsigned int min_ratio;
unsigned int max_ratio, max_prop_frac;
--- linux-next.orig/mm/backing-dev.c 2011-06-19 22:59:49.000000000 +0800
+++ linux-next/mm/backing-dev.c 2011-06-19 22:59:53.000000000 +0800
@@ -670,8 +670,6 @@ int bdi_init(struct backing_dev_info *bd
goto err;
}
- bdi->dirty_exceeded = 0;
-
bdi->bw_time_stamp = jiffies;
bdi->written_stamp = 0;
--
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