Re: 2.4.20: Proccess stuck in __lock_page ...

[Jens Axboe <axboe@suse.de>]

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