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SubjectRe: [PATCH] O_DIRECT with hardware blocksize alignment
On Tue, Jan 15, 2002 at 01:20:26PM +0100, Andrea Arcangeli wrote:
> > 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
>
> in the kiovec yes, but in the same request queue there will be also the
> concurrent requests from the filesystem, and they will have different
> b_size, see Jens's mail about different b_size merged in the same
> request.

Ok, I've read over Badri's latest patch, and it would seem he
assumes that the kiovec coming into brw_kiovec has buffer_heads of
512bytes (as raw.c would prepare). He then submits the I/O in differing
chunks (eg 2048 + 4096 + 4096 + 2048 for a 2048-aligned buffer).
Correct me if I am wrong (I can't see anything in raw.c that would
change the sizes in the kiovec).
For O_DIRECT, the fallback is s_blocksize, not the hardware
minimum of 512. So the kiovec would be coming into brw_kiovec with a
b_size of 4096 or so. My patch lets b_size be anything between 512 and
s_blocksize.
To work with Badri's code, would not the O_DIRECT path want to
submit a kiovec that is entirely b_size = 512 and let brw_kiovec handle
expanding it to larger sizes? This makes my patch simpler, but I wonder
what issues that presents.

Joel

--

"When choosing between two evils, I always like to try the one
I've never tried before."
- Mae West

http://www.jlbec.org/
jlbec@evilplan.org
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