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

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