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Re: [dm-devel] [PATCH 2/3] Introduce percpu rw semaphores

From: "Paul E. McKenney" <paulmck linux vnet ibm com>
To: Mikulas Patocka <mpatocka redhat com>
Cc: Jens Axboe <axboe kernel dk>, Andrea Arcangeli <aarcange redhat com>, Jan Kara <jack suse cz>, Eric Dumazet <eric dumazet gmail com>, linux-kernel vger kernel org, Jeff Moyer <jmoyer redhat com>, dm-devel redhat com, Alexander Viro <viro zeniv linux org uk>, kosaki motohiro jp fujitsu com, linux-fsdevel vger kernel org, lwoodman redhat com, "Alasdair G. Kergon" <agk redhat com>
Subject: Re: [dm-devel] [PATCH 2/3] Introduce percpu rw semaphores
Date: Wed, 1 Aug 2012 10:15:27 -0700

On Mon, Jul 30, 2012 at 08:00:19PM -0400, Mikulas Patocka wrote:
> 
> 
> On Mon, 30 Jul 2012, Paul E. McKenney wrote:
> 
> > On Sun, Jul 29, 2012 at 01:13:34AM -0400, Mikulas Patocka wrote:
> > > On Sat, 28 Jul 2012, Eric Dumazet wrote:
> > > > On Sat, 2012-07-28 at 12:41 -0400, Mikulas Patocka wrote:
> > 
> > [ . . . ]
> > 
> > > > (bdev->bd_block_size should be read exactly once )
> > > 
> > > Rewrite all direct and non-direct io code so that it reads block size just 
> > > once ...
> > 
> > For whatever it is worth, the 3.5 Linux kernel only has about ten mentions
> > of bd_block_size, at least according to cscope.
> 
> plus 213 uses of i_blkbits (which is derived directly from bd_block_size). 
> 45 of them is in fs/*.c and mm/*.c

At least it is only hundreds rather than thousands!  ;-)

							Thanx, Paul

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