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

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

[Christoph Hellwig]

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.


Signed-off-by: Christoph Hellwig <hch@lst.de>

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);

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

[Jens Axboe]

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.

-- 
Jens Axboe

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

[Christoph Hellwig]

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?


Signed-off-by: Christoph Hellwig <hch@lst.de>

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);

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@suse.de>

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> 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