Re: [PATCH V3] bio: modify __bio_add_page() to accept pages that don't start a new segment

[Ming Lei]

On Tue, May 27, 2014 at 7:58 PM, Maurizio Lombardi <mlombard@xxxxxxxxxx> wrote:
> On Tue, May 27, 2014 at 06:15:45PM +0800, Ming Lei wrote:
>>
>> If the page can be merged to last segment, it should have been
>> covered by code in branch of 'if (bio->bi_vcnt > 0) ...', shouldn't it?
>>
>> Or maybe it is better to make that code cover your case since
>> looks your case is similar with that one according to your commit
>> log.
>>
>
> I realized that maybe you mean this branch:
>
> if (bio->bi_vcnt > 1 && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec)))
>
> right?
> In this case the branch is not even reached in the original code because
> the function returned an error way before executing it (line 760)
>
> There was already a patchset trying to modify the code in a different way than mine:
>
> https://groups.google.com/forum/#!msg/linux.kernel/3IanUpBVhFQ/3Xbg3yLRFp4J
>
> but it has been ignored and in my opinion it takes a more
> complicated approach.

Looks your approach is simpler.

But looks there is one problem if I understand correctly:
__blk_recalc_rq_segments() may not cover the last vector
because bio->bi_iter.bi_size isn't updated until the end of
__bio_add_page().

But it shouldn't have been related with current virtio-blk problem.

Thanks,
-- 
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/