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@xxxxxxxxx> --- mm/page-writeback.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) --- linux-next.orig/mm/page-writeback.c 2011-08-29 19:08:43.000000000 +0800 +++ linux-next/mm/page-writeback.c 2011-08-29 19:08:44.000000000 +0800 @@ -1193,7 +1193,20 @@ pause: if (!dirty_exceeded && bdi->dirty_exceeded) bdi->dirty_exceeded = 0; - current->nr_dirtied_pause = dirty_poll_interval(nr_dirty, dirty_thresh); + if (pause == 0) + current->nr_dirtied_pause = + dirty_poll_interval(nr_dirty, dirty_thresh); + else if (period <= 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 * 3/8)/HZ, + pages_dirtied / 4, + pages_dirtied * 7/8); if (writeback_in_progress(bdi)) return; -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
