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From: Alan Stern <stern@rowland.harvard.edu>
To: Douglas Gilbert <dougg@torque.net>
Cc: Joerg Schilling <Joerg.Schilling@fokus.fraunhofer.de>,
	<linux-kernel@vger.kernel.org>, <jens.axboe@oracle.com>,
	<James.Bottomley@steeleye.com>
Subject: Re: [PATCH] Block layer: separate out queue-oriented ioctls
Date: Tue, 20 Feb 2007 10:55:45 -0500 (EST)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.0702201052360.4992-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <45DA7D77.9020709@torque.net>

On Mon, 19 Feb 2007, Douglas Gilbert wrote:

> > Come to think of it, the reserved_size value used when a new sg device is
> > created should also be capped at max_sectors * 512.  Agreed?  I can't see
> > any reason for ever having a larger buffer -- it would be impossible to
> > make use of the extra space.
> 
> Alan,
> That depends whether or not max_sectors can be changed
> (via sysfs) subsequent to a sg device being created.
> And I think it can.
> 
> # ls -l /sys/block/sdc/queue/
> total 0
> drwxr-xr-x 2 root root    0 Feb 19 18:29 iosched
> -r--r--r-- 1 root root 4096 Feb 19 23:41 max_hw_sectors_kb
> -rw-r--r-- 1 root root 4096 Feb 19 23:41 max_sectors_kb
> -rw-r--r-- 1 root root 4096 Feb 19 23:41 nr_requests
> -rw-r--r-- 1 root root 4096 Feb 19 23:41 read_ahead_kb
> -rw-r--r-- 1 root root 4096 Feb 19 23:41 scheduler

Yes, it definitely can be changed.

> # cat max_hw_sectors_kb > max_sectors_kb
> 
> ... is the real maximum if the LLD that set max_hw_sectors_kb
> is to be believed (actually it is often a finger in
> the wind).

That's why my patch computes the minimum value every time the 
GET_RESERVED_SIZE ioctl runs -- in case max_sectors has changed.

If the user decides to increase max_sectors, then the reserved_size can be 
increased immediately afterward.  This shouldn't cause any problems.

I will submit a revised patch shortly, on the linux-scsi list.

Alan Stern


  reply	other threads:[~2007-02-20 15:55 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-16 19:37 Alan Stern
2007-02-17  6:28 ` Jens Axboe
2007-02-17 21:18   ` Joerg Schilling
2007-02-18  3:43   ` Douglas Gilbert
2007-02-18 12:37     ` Joerg Schilling
2007-02-18 16:44     ` Alan Stern
2007-02-18 18:27       ` Joerg Schilling
2007-02-19 16:06         ` Alan Stern
2007-02-19 16:08           ` Joerg Schilling
2007-02-19 17:06             ` Alan Stern
2007-02-19 22:25               ` Douglas Gilbert
2007-02-20  3:48                 ` Alan Stern
2007-02-20  4:47                   ` Douglas Gilbert
2007-02-20 15:55                     ` Alan Stern [this message]
2007-04-26  9:19                 ` Joerg Schilling
2007-04-26 15:04                   ` Alan Stern
2007-04-26 15:08                     ` James Bottomley

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