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SubjectRe: [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler
On Tue, Feb 12 2008, Andrew Morton wrote:
> On Sat, 09 Feb 2008 08:30:40 -0500
> Paul Clements <paul.clements@steeleye.com> wrote:
>
> > + old_e = disk->queue->elevator;
> > + if (elevator_init(disk->queue, "deadline") == 0 ||
> > + elevator_init(disk->queue, "noop") == 0) {
> > + elevator_exit(old_e);
> > + }
> > }
>
> afacit elevator_init() will not trigger a request_module(). And you really
> do want to trigger the request_module() here. Perhaps the block layer
> should provide a means of doing so?

Good point, I think elevator_get() should do that automatically. Does
this look sane?

diff --git a/block/elevator.c b/block/elevator.c
index bafbae0..88318c3 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -134,6 +134,21 @@ static struct elevator_type *elevator_get(const char *name)
spin_lock(&elv_list_lock);

e = elevator_find(name);
+ if (!e) {
+ char elv[ELV_NAME_MAX + strlen("-iosched")];
+
+ spin_unlock(&elv_list_lock);
+
+ if (!strcmp(name, "anticipatory"))
+ sprintf(elv, "as-iosched");
+ else
+ sprintf(elv, "%s-iosched", name);
+
+ request_module(elv);
+ spin_lock(&elv_list_lock);
+ e = elevator_find(name);
+ }
+
if (e && !try_module_get(e->elevator_owner))
e = NULL;

--
Jens Axboe



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