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SubjectRe: PATCH 3/6 - direct-io: do not merge logically non-contiguous requests
On Wed, Aug 11, 2010 at 09:27:45AM -0400, Jeff Moyer wrote:
> Josef Bacik <josef@redhat.com> writes:
>
> > So say blocksize of 4k, we do dio to 12k, the first time around
> > dio->block_in_file is 0, we set dio->cur_page, and move on to the next page, and
> > bio->block_in_file is set to 1. We find that dio->cur_page is set, so we do
> > dio_send_cur_page(). Since !dio->bio we create a new bio, and set
> > dio->logical_offset_in_bio to 0, since thats the offset of dio->cur_page. Then
> > we setup the next cur_page as the page for logical block 1, and
> > dio->block_in_file gets bumped to 2. We map the next block and come into
> > dio_send_cur_page() again. At this point cur_offset would be 8192...and shit I
> > just realized what was wrong. If you change
> >
> > loff_t cur_offset = dio->block_in_file << dio->blkbits;
> >
> > to
> >
> > loff_t cur_offset = dio->cur_page_fs_offset << dio->blkbits;
>
> Sorry, I wasn't very clear in my description, but you figured it out.
> ;-) Of course, cur_page_fs_offset is already in bytes, so that left
> shift is not necessary.
>

Ah right, sorry.

> > That should fix the problem. Sorry guys, I screwed that up. I'll look at this
> > again tomorrow after I've had my 2 hours of sleep and see if this all still
> > makes sense, but I think the above should fixe the performance thing. As for
> > the dio->boundary thing, dio_bio_submit() sets dio->boundary to 0, so the same
> > bio won't be submitted twice.
>
> While I don't doubt that you are right, I will sleep better at night if
> we do an else if. (To be fair, this ambiguity was not introduced by
> you).
>
> I've tested this patch, added printk's and watched blktrace to verify
> that we don't split up I/Os. So long as no one objects, I'll post this
> for inclusion in a new thread.
>
> Thanks for looking into it, Josef.
>

No problem, thanks for making me look at it again. You can add

Acked-by: Josef Bacik <josef@redhat.com>

Thanks,

Josef


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