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From: Andrew Morton <akpm@linux-foundation.org>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Paul Clements <paul.clements@steeleye.com>,
	randy.dunlap@oracle.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler
Date: Mon, 18 Feb 2008 15:50:01 -0800	[thread overview]
Message-ID: <20080218155001.97bf5976.akpm@linux-foundation.org> (raw)
In-Reply-To: <20080218181630.GI23197@kernel.dk>

On Mon, 18 Feb 2008 19:16:30 +0100 Jens Axboe <jens.axboe@oracle.com> wrote:

> 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;

Looks nice and simple.  There might be some of the usual ordering problems
when this is called during boot, maybe is-initramfs-available-yet problems,
etc.  But it's unlikely to make things regress from where they are now.

Should we emit a warning if the desired elevator wasn't available?

  reply	other threads:[~2008-02-18 23:51 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 16:47 Paul Clements
2008-02-08 17:33 ` Randy Dunlap
2008-02-08 18:11   ` Andrew Morton
2008-02-08 18:41     ` Paul Clements
2008-02-08 20:45       ` Jens Axboe
2008-02-08 20:47         ` Jens Axboe
2008-02-08 21:23           ` Paul Clements
2008-02-08 22:02             ` Andrew Morton
2008-02-09 13:30               ` Paul Clements
2008-02-12 23:16                 ` Andrew Morton
2008-02-18 18:16                   ` Jens Axboe
2008-02-18 23:50                     ` Andrew Morton [this message]
2008-02-19  9:19                       ` Jens Axboe
2008-02-19  9:24                         ` Jens Axboe
2008-02-19 10:02                           ` Andrew Morton
2008-02-19 10:05                             ` Jens Axboe
2008-02-08 22:45       ` [Nbd] " Mike Snitzer

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