linux-kernel - Re: [PATCH 12/20] nbd: limit blk

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Message-ID: <20060912224708.GA23515@kernel.dk>
Date:	Wed, 13 Sep 2006 00:47:08 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	David Miller <davem@...emloft.net>,
	Rik van Riel <riel@...hat.com>,
	Daniel Phillips <phillips@...gle.com>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 12/20] nbd: limit blk_queue

On Tue, Sep 12 2006, Peter Zijlstra wrote:
> Limit each request to 1 page, so that the request throttling also limits the
> number of in-flight pages.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Signed-off-by: Daniel Phillips <phillips@...gle.com>
> CC: Pavel Machek <pavel@....cz>
> ---
>  drivers/block/nbd.c |   17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/drivers/block/nbd.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/nbd.c	2006-09-07 18:43:41.000000000 +0200
> +++ linux-2.6/drivers/block/nbd.c	2006-09-07 18:44:12.000000000 +0200
> @@ -638,6 +638,9 @@ static int __init nbd_init(void)
>  			put_disk(disk);
>  			goto out;
>  		}
> +		blk_queue_max_segment_size(disk->queue, PAGE_SIZE);
> +		blk_queue_max_hw_segments(disk->queue, 1);
> +		blk_queue_max_phys_segments(disk->queue, 1);

Another bandaid. What happens if nr_requests number of pages is still
too many for a system? You just moved whatever problem you had, you
didn't solve anything.

-- 
Jens Axboe

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