Re: [PATCH] move tasklist walk from cfq-iosched to elevator.c

[Jens Axboe]

On Mon, Sep 19 2005, Christoph Hellwig wrote:
> On Fri, Aug 26, 2005 at 03:45:10PM +0200, Jens Axboe wrote:
> > On Fri, Aug 26 2005, Christoph Hellwig wrote:
> > > We're trying to get rid of as much as possible tasklist walks, or at
> > > least moving them to core code.  This patch falls into the second
> > > category.
> > > 
> > > Instead of walking the tasklist in cfq-iosched move that into
> > > elv_unregister.  The added benefit is that with this change the as
> > > ioscheduler might be might unloadable more easily aswell.
> > > 
> > > The new code uses read_lock instead of read_lock_irq because the
> > > tasklist_lock only needs irq disabling for writers.
> > 
> > Looks innocent enough, fine with me. 'as' will need additional work to
> > be unloadable, but it wont break anything since it's running with an
> > elevated module count right now anyways.
> 
> any chance to send this on to akpm?

Sure, already ack'ed it and I thought akpm was cc'ed on the mail.
Anyways, andrew can you add this? Thanks!

Signed-off-by: Jens Axboe <axboe@xxxxxxx>

> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> 
> Index: linux-2.6/drivers/block/as-iosched.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/as-iosched.c	2005-08-11 16:45:55.000000000 +0200
> +++ linux-2.6/drivers/block/as-iosched.c	2005-08-14 12:13:08.000000000 +0200
> @@ -2119,8 +2119,8 @@
>  
>  static void __exit as_exit(void)
>  {
> -	kmem_cache_destroy(arq_pool);
>  	elv_unregister(&iosched_as);
> +	kmem_cache_destroy(arq_pool);
>  }
>  
>  module_init(as_init);
> Index: linux-2.6/drivers/block/cfq-iosched.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/cfq-iosched.c	2005-08-11 16:45:55.000000000 +0200
> +++ linux-2.6/drivers/block/cfq-iosched.c	2005-08-14 12:09:17.000000000 +0200
> @@ -2609,28 +2609,8 @@
>  
>  static void __exit cfq_exit(void)
>  {
> -	struct task_struct *g, *p;
> -	unsigned long flags;
> -
> -	read_lock_irqsave(&tasklist_lock, flags);
> -
> -	/*
> -	 * iterate each process in the system, removing our io_context
> -	 */
> -	do_each_thread(g, p) {
> -		struct io_context *ioc = p->io_context;
> -
> -		if (ioc && ioc->cic) {
> -			ioc->cic->exit(ioc->cic);
> -			cfq_free_io_context(ioc->cic);
> -			ioc->cic = NULL;
> -		}
> -	} while_each_thread(g, p);
> -
> -	read_unlock_irqrestore(&tasklist_lock, flags);
> -
> -	cfq_slab_kill();
>  	elv_unregister(&iosched_cfq);
> +	cfq_slab_kill();
>  }
>  
>  module_init(cfq_init);
> Index: linux-2.6/drivers/block/elevator.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/elevator.c	2005-08-11 16:45:55.000000000 +0200
> +++ linux-2.6/drivers/block/elevator.c	2005-08-14 12:12:35.000000000 +0200
> @@ -572,6 +572,27 @@
>  
>  void elv_unregister(struct elevator_type *e)
>  {
> +	struct task_struct *g, *p;
> +
> +	/*
> +	 * Iterate every thread in the process to remove the io contexts.
> +	 */
> +	read_lock(&tasklist_lock);
> +	do_each_thread(g, p) {
> +		struct io_context *ioc = p->io_context;
> +		if (ioc && ioc->cic) {
> +			ioc->cic->exit(ioc->cic);
> +			ioc->cic->dtor(ioc->cic);
> +			ioc->cic = NULL;
> +		}
> +		if (ioc && ioc->aic) {
> +			ioc->aic->exit(ioc->aic);
> +			ioc->aic->dtor(ioc->aic);
> +			ioc->aic = NULL;
> +		}
> +	} while_each_thread(g, p);
> +	read_unlock(&tasklist_lock);
> +
>  	spin_lock_irq(&elv_list_lock);
>  	list_del_init(&e->list);
>  	spin_unlock_irq(&elv_list_lock);
> 

-- 
Jens Axboe

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