linux-kernel - Re: [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler

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Date:	Mon, 18 Feb 2008 19:16:30 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Paul Clements <paul.clements@...eleye.com>,
	randy.dunlap@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [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@...eleye.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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