Re: [PATCH] O_DIRECT with hardware blocksize alignment

[Joel Becker]

On Sat, Jan 12, 2002 at 01:31:22PM +0100, Andrea Arcangeli wrote:
> On Wed, Jan 09, 2002 at 07:56:07PM +0000, Joel Becker wrote:
> > min(I/O alignment, s_blocksize) is used as the effective
> > blocksize.  eg:
> > 
> > I/O alignment	s_blocksize	final blocksize
> > 8192		4096		4096
> > 4096		4096		4096
> > 512		4096		512
> 
> this falls in the same risky category of the vary-I/O patch from Badari
> (check the discussion on l-k) for rawio, so to make it safe it also will

	How so?  All I/O is at the computed blocksize.  In every
request, the size of each I/O in the kiovec is the same.  The
computation is done upon entrance to generic_file_direct_IO, and it is
kept that way.  You don't have bh[0]->b_size = 512; bh[1]->b_size =
4096;
	Hmm, maybe you mean things like that rumoured 3-ware issue.  I
dunno.  I do know that this code seems to work just fine with ide,
aha7xxx, and the qlogic driver.  Certain software really wants to use
O_DIRECT, and they align I/O on 512byte boundaries.  So any scheme that
fails this when it doesn't have to is a problem.

> aligned I/O, but still large I/O) So I suggest you to check Badari's
> stuff and the thread on l-k and to make a new patch incremental with his

	I've added myself to that thread as well.

Joel

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