Re: 64-bit capable block device layer

From: Stephen C. Tweedie (sct@redhat.com)
Date: Thu Mar 08 2001 - 07:14:17 EST


Hi,

On Wed, Mar 07, 2001 at 07:53:23PM +0100, Jens Axboe wrote:
> >
> > OTOH, I'm not sure what problems it could give to make this
> > a compile-time option...
>
> Plus compile time options are nasty :-). It would probably make
> bigger sense to completely skip all the merging etc for low end
> machines. I think they already do this for embedded kernels (ie
> removing ll_rw_blk.c and elevator.c). That avoids most of the
> 64-bit arithmetic anyway.

It's not just a sector-number and ll_rw_blk/elevator issue. The limit
goes all the way up to the users of the block device, be they the
filesystem, buffer cache or block read/write layer.

This is especially true for filesystems like XFS which need a 512-byte
blocksize. At least with ext2 you can set the blocksize to 4kB and
get some of the benefit of larger block devices without having to
overflow the 32-bit block number.

Cheers,
 Stephen
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