Re: [PATCH 2/4] block: check virt boundary in bio_will_gap()

[Sagi Grimberg]

> > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > > index 4571ef1..b8ff6a3 100644
> > > --- a/include/linux/blkdev.h
> > > +++ b/include/linux/blkdev.h
> > > @@ -1388,7 +1388,7 @@ static inline bool bvec_gap_to_prev(struct
> > > request_queue *q,
> > >    static inline bool bio_will_gap(struct request_queue *q, struct bio
> > > *prev,
> > >                           struct bio *next)
> > >    {
> > > -       if (!bio_has_data(prev))
> > > +       if (!bio_has_data(prev) || !queue_virt_boundary(q))
> > >    bio_integrity_add_page              return false;
> >
> >
> > Can we not do that?
>
> Given there are only 3 drivers which set virt boundary, I think
> it is reasonable to do that.

3 drivers that are really performance critical. I don't think we
should add optimized branching for some of the drivers especially
when the drivers that do set virt_boundary *really* care about latency.

> > bvec_gap_to_prev is already checking the virt_boundary and I'd sorta
> > like to keep the motivation to optimize bio_get_last_bvec() to be O(1).
>
> Currently the approaches I thought of still need to iterate bvec by bvec,
> not sure if O(1) can be reached easily, but I am happy to discuss the
> optimized implementation.

Me too. Note that I don't mind if the bio split code won't be optimized,
but I do want req_gap_back_merge/req_gap_front_merge to be...

Also, are the bvec_gap_to_prev usages in bio_add_pc_page and
bio_integrity_add_page safe? I didn't test this stuff with integrity
payloads...