Re: [PATCH 07/10] writeback: dirty ratelimit - think time compensation

Wu Fengguang
2011-08-26T12:05:49Z

> - pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
> + period = (HZ * pages_dirtied) / (task_ratelimit | 1);
> + pause = current->dirty_paused_when + period - now;
> + /*
> + * For less than 1s think time (ext3/4 may block the dirtier
> + * for up to 800ms from time to time on 1-HDD; so does xfs,
> + * however at much less frequency), try to compensate it in
> + * future periods by updating the virtual time; otherwise just
> + * do a reset, as it may be a light dirtier.
> + */
> + if (unlikely(pause <= 0)) {
> + if (pause < -HZ) {
> + current->dirty_paused_when = now;
> + current->nr_dirtied = 0;
> + } else if (period) {
> + current->dirty_paused_when += period;
> + current->nr_dirtied = 0;
> + }

> + pause = 1; /* avoid resetting nr_dirtied_pause below */

Note: the above comment is only effective with the planned max pause
time adaption patch.

Thanks,
Fengguang

> + break;
> + }
> pause = min(pause, (long)MAX_PAUSE);
>
> pause:
> __set_current_state(TASK_UNINTERRUPTIBLE);
> io_schedule_timeout(pause);
>
> + current->dirty_paused_when = now + pause;
> + current->nr_dirtied = 0;
> +
> dirty_thresh = hard_dirty_limit(dirty_thresh);
> /*
> * max-pause area. If dirty exceeded but still within this
> @@ -1017,7 +1046,6 @@ pause:
> if (!dirty_exceeded && bdi->dirty_exceeded)
> bdi->dirty_exceeded = 0;
>
> - current->nr_dirtied = 0;
> current->nr_dirtied_pause = dirty_poll_interval(nr_dirty, dirty_thresh);
>
> if (writeback_in_progress(bdi))
> --- linux-next.orig/kernel/fork.c 2011-08-16 08:50:41.000000000 +0800
> +++ linux-next/kernel/fork.c 2011-08-16 08:54:13.000000000 +0800
> @@ -1303,6 +1303,7 @@ static struct task_struct *copy_process(
>
> p->nr_dirtied = 0;
> p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
> + p->dirty_paused_when = 0;
>
> /*
> * Ok, make it visible to the rest of the system.
>