[PATCH for-4.4] block: split bios to max possible length

[Keith Busch]

On Wed, Jan 06, 2016 at 02:53:22PM +0800, Ming Lei wrote:
> On Wed, Jan 6, 2016 at 2:29 PM, Ming Lei <tom.leiming at gmail.com> wrote:
> >
> > bvec_iter_advance() can split anywhere, but the splitted bios may
> > cross one same bvec, which may cause trouble, 

Cross? One starts where the other starts. Could you please explain what's
wrong?

> > for example,
> > BIOVEC_PHYS_MERGEABLE() may not work well and
> > blk_phys_contig_segment() too.

Could you please explain why it may not work well? I have no idea what
concern you have with BIOVEC_PHYS_MERGEABLE in this case.

The only place blk_phys_contig_segment is called from is
ll_merge_requests, and the first req of the split bio wouldn't even go
through here because it's marked REQ_NOMERGE.

> blk_rq_map_sg() isn't ready for splitting in the middle of bvec too.

Could you please explain? It just uses the bio iterator, which I'm pretty
sure is not broken.