On Thu, 2010-06-17 at 20:04 +0200, Jan Kara wrote:
> +/* Wait until write_chunk is written or we get below dirty limits */
> +void bdi_wait_written(struct backing_dev_info *bdi, long write_chunk)
> +{
> + struct bdi_written_count wc = {
> + .list = LIST_HEAD_INIT(wc.list),
> + .written = write_chunk,
> + };
> + DECLARE_WAITQUEUE(wait, current);
> + int pause = 1;
> +
> + bdi_add_writer(bdi, &wc, &wait);
> + for (;;) {
> + if (signal_pending_state(TASK_KILLABLE, current))
> + break;
> +
> + /*
> + * Make the task just killable so that tasks cannot circumvent
> + * throttling by sending themselves non-fatal signals...
> + */
> + __set_current_state(TASK_KILLABLE);
> + io_schedule_timeout(pause);
> +
> + /*
> + * The following check is save without wb_written_wait.lock
> + * because once bdi_remove_writer removes us from the list
> + * noone will touch us and it's impossible for list_empty check
> + * to trigger as false positive. The barrier is there to avoid
> + * missing the wakeup when we are removed from the list.
> + */
> + smp_rmb();
> + if (list_empty(&wc.list))
> + break;
> +
> + if (!dirty_limits_exceeded(bdi))
> + break;
> +
> + /*
> + * Increase the delay for each loop, up to our previous
> + * default of taking a 100ms nap.
> + */
> + pause <<= 1;
> + if (pause > HZ / 10)
> + pause = HZ / 10;
> + }
> +
> + spin_lock_irq(&bdi->wb_written_wait.lock);
> + __remove_wait_queue(&bdi->wb_written_wait, &wait);
> + if (!list_empty(&wc.list))
> + bdi_remove_writer(bdi, &wc);
> + spin_unlock_irq(&bdi->wb_written_wait.lock);
> +}
OK, so the whole pause thing is simply because we don't get a wakeup
when we drop below the limit, right?
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