Re: 2.4.20: Proccess stuck in __lock_page ...

Jens Axboe
2003-05-28T10:12:37Z

On Wed, May 28 2003, Andrew Morton wrote:
> Matthias Mueller <matthias.mueller@rz.uni-karlsruhe.de> wrote:
> >
> > Works fine on my notebook. Good throughput and no mouse hangs anymore.
>
> Interesting.
>
> Could you please work out which change caused it? Go back to stock 2.4 and
> then apply this:
>
>
> diff -puN drivers/block/ll_rw_blk.c~1 drivers/block/ll_rw_blk.c
> --- 24/drivers/block/ll_rw_blk.c~1 2003-05-28 03:20:42.000000000 -0700
> +++ 24-akpm/drivers/block/ll_rw_blk.c 2003-05-28 03:20:57.000000000 -0700
> @@ -590,10 +590,10 @@ static struct request *__get_request_wai
> register struct request *rq;
> DECLARE_WAITQUEUE(wait, current);
>
> - generic_unplug_device(q);
> add_wait_queue_exclusive(&q->wait_for_requests[rw], &wait);
> do {
> set_current_state(TASK_UNINTERRUPTIBLE);
> + generic_unplug_device(q);
> if (q->rq[rw].count == 0)
> schedule();
> spin_lock_irq(&io_request_lock);

I think it was already established that this wasn't the reason. Was my
first suspect too, though...

> then this:
>
> diff -puN drivers/block/ll_rw_blk.c~2 drivers/block/ll_rw_blk.c
> --- 24/drivers/block/ll_rw_blk.c~2 2003-05-28 03:21:03.000000000 -0700
> +++ 24-akpm/drivers/block/ll_rw_blk.c 2003-05-28 03:21:09.000000000 -0700
> @@ -590,7 +590,7 @@ static struct request *__get_request_wai
> register struct request *rq;
> DECLARE_WAITQUEUE(wait, current);
>
> - add_wait_queue_exclusive(&q->wait_for_requests[rw], &wait);
> + add_wait_queue(&q->wait_for_requests[rw], &wait);
> do {
> set_current_state(TASK_UNINTERRUPTIBLE);
> generic_unplug_device(q);

Since we do a general wake_up(), only the order of wakeups matter here
right (lifo vs fifo). Given that, the _exclusive() should be more fair
possibly at the cost of a bit of throughput.

> Then this (totally unlikely, don't bother):
>
> diff -puN drivers/block/ll_rw_blk.c~3 drivers/block/ll_rw_blk.c
> --- 24/drivers/block/ll_rw_blk.c~3 2003-05-28 03:21:15.000000000 -0700
> +++ 24-akpm/drivers/block/ll_rw_blk.c 2003-05-28 03:21:39.000000000 -0700
> @@ -829,8 +829,7 @@ void blkdev_release_request(struct reque
> */
> if (q) {
> list_add(&req->queue, &q->rq[rw].free);
> - if (++q->rq[rw].count >= q->batch_requests &&
> - waitqueue_active(&q->wait_for_requests[rw]))
> + if (++q->rq[rw].count >= q->batch_requests)
> wake_up(&q->wait_for_requests[rw]);
> }
> }

Well it's the only one left :). But you are right, try one of them at
the time, establishing the effect of each of them.

--
Jens Axboe