[PATCH 1/2] block: accumulate segment page gaps per bio

[Keith Busch]

On Wed, Aug 06, 2025 at 04:53:34PM +0200, Christoph Hellwig wrote:
> On Tue, Aug 05, 2025 at 04:52:11PM -0600, Keith Busch wrote:
> > On Tue, Aug 05, 2025 at 12:56:07PM -0700, Keith Busch wrote:
> > > +	bv = next->bio->bi_io_vec[0];
> > > +	bvprv = req->biotail->bi_io_vec[req->biotail->bi_vcnt - 1];
> > 
> > Hm, commit 7bcd79ac50d9d8 suggests I missed something obvious about not
> > being allowed to use 'bi_vcnt - 1' for the tail bvec of the previous
> > bio. I guess it's some stacking thing.
> 
> It is bio cloning and splitting.  bi_io_vec is the original payload added
> to a bio, and directly accessing it is only allowed for the submitter,
> i.e. usually the file system.  The I/O stack always need to go through
> the bio_iter to deal with split/cloned/truncated/partially completed and
> resubmitted bios.

Yeah, I knew about the splitting, but I am only using this for merging,
and bio's split off the front can't merge, so thought I was okay.

But the cloning, yes, I messed that up. v2 is sent with a fix for it.
Sorry for the rapid fire versions; I realized you were travelling, so I
didn't expect more feedback on v1. But thank you for finding some time
to review anyway.