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SubjectRe: [PATCH] move tasklist walk from cfq-iosched to elevator.c
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);
-
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