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

[Keith Busch <kbusch@kernel.org>]

On Wed, Aug 06, 2025 at 04:56:21PM +0200, Christoph Hellwig wrote:
> > index 0a29b20939d17..d0ed28d40fe02 100644
> > --- a/include/linux/blk_types.h
> > +++ b/include/linux/blk_types.h
> > @@ -264,6 +264,8 @@ struct bio {
> >  
> >  	unsigned short		bi_max_vecs;	/* max bvl_vecs we can hold */
> >  
> > +	unsigned int		page_gaps;	/* a mask of all the vector gaps */
> 
> Bloating the bio for the gaps, especially as the bio is otherwise not
> built to hardware limits at all seems like an odd tradeoff.

Maybe, but I don't have anywhere else to put this. We split the bio to
its hardware limits at some point, which is where this field gets
initially set.

It doesn't need to be a mask (though that conceptually is the most
intuitive). It really just needs to indicate the lowest set bit of any
page gap between segments. There is a one byte hole in the bio that can
fit it without changing the bio size.