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authorWu Fengguang <fengguang.wu@intel.com>2011-06-11 19:32:32 -0600
committerWu Fengguang <fengguang.wu@intel.com>2011-10-03 21:08:58 +0800
commit57fc978cfb61ed40a7bbfe5a569359159ba31abd (patch)
tree870ffd08e0c1bb0dde55e4f1ed4dfa2bda8e3a80 /mm
parentc8462cc9de9e92264ec647903772f6036a99b286 (diff)
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writeback: control dirty pause time
The dirty pause time shall ultimately be controlled by adjusting nr_dirtied_pause, since there is relationship pause = pages_dirtied / task_ratelimit Assuming pages_dirtied ~= nr_dirtied_pause task_ratelimit ~= dirty_ratelimit We get nr_dirtied_pause ~= dirty_ratelimit * desired_pause Here dirty_ratelimit is preferred over task_ratelimit because it's more stable. It's also important to limit possible large transitional errors: - bw is changing quickly - pages_dirtied << nr_dirtied_pause on entering dirty exceeded area - pages_dirtied >> nr_dirtied_pause on btrfs (to be improved by a separate fix, but still expect non-trivial errors) So we end up using the above formula inside clamp_val(). The best test case for this code is to run 100 "dd bs=4M" tasks on btrfs and check its pause time distribution. Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Diffstat (limited to 'mm')
-rw-r--r--mm/page-writeback.c20
1 files changed, 19 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index cc351e6f9ed9..6a8bb693b429 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1086,6 +1086,10 @@ static void balance_dirty_pages(struct address_space *mapping,
task_ratelimit = (u64)dirty_ratelimit *
pos_ratio >> RATELIMIT_CALC_SHIFT;
pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
+ if (unlikely(pause <= 0)) {
+ pause = 1; /* avoid resetting nr_dirtied_pause below */
+ break;
+ }
pause = min(pause, max_pause);
pause:
@@ -1107,7 +1111,21 @@ pause:
bdi->dirty_exceeded = 0;
current->nr_dirtied = 0;
- current->nr_dirtied_pause = dirty_poll_interval(nr_dirty, dirty_thresh);
+ if (pause == 0) { /* in freerun area */
+ current->nr_dirtied_pause =
+ dirty_poll_interval(nr_dirty, dirty_thresh);
+ } else if (pause <= max_pause / 4 &&
+ pages_dirtied >= current->nr_dirtied_pause) {
+ current->nr_dirtied_pause = clamp_val(
+ dirty_ratelimit * (max_pause / 2) / HZ,
+ pages_dirtied + pages_dirtied / 8,
+ pages_dirtied * 4);
+ } else if (pause >= max_pause) {
+ current->nr_dirtied_pause = 1 | clamp_val(
+ dirty_ratelimit * (max_pause / 2) / HZ,
+ pages_dirtied / 4,
+ pages_dirtied - pages_dirtied / 8);
+ }
if (writeback_in_progress(bdi))
return;