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author | Wu Fengguang <fengguang.wu@intel.com> | 2011-06-12 01:32:32 (GMT) |
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committer | Wu Fengguang <fengguang.wu@intel.com> | 2011-10-03 13:08:58 (GMT) |
commit | 57fc978cfb61ed40a7bbfe5a569359159ba31abd (patch) | |
tree | 870ffd08e0c1bb0dde55e4f1ed4dfa2bda8e3a80 | |
parent | c8462cc9de9e92264ec647903772f6036a99b286 (diff) | |
download | linux-fsl-qoriq-57fc978cfb61ed40a7bbfe5a569359159ba31abd.tar.xz |
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>
-rw-r--r-- | mm/page-writeback.c | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index cc351e6..6a8bb69 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; |