[PATCHv6 07/11] block/bounce: count bytes instead of sectors

[Keith Busch]

On Fri, Jul 22, 2022 at 03:01:06PM -0700, Bart Van Assche wrote:
> On 6/10/22 12:58, Keith Busch wrote:
> > From: Keith Busch <kbusch at kernel.org>
> > 
> > Individual bv_len's may not be a sector size.
> > 
> > Signed-off-by: Keith Busch <kbusch at kernel.org>
> > Reviewed-by: Damien Le Moal <damien.lemoal at opensource.wdc.com>
> > Reviewed-by: Pankaj Raghav <p.raghav at samsung.com>
> > ---
> >   block/bounce.c | 13 ++++++++++---
> >   1 file changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/block/bounce.c b/block/bounce.c
> > index 8f7b6fe3b4db..fbadf179601f 100644
> > --- a/block/bounce.c
> > +++ b/block/bounce.c
> > @@ -205,19 +205,26 @@ void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> >   	int rw = bio_data_dir(*bio_orig);
> >   	struct bio_vec *to, from;
> >   	struct bvec_iter iter;
> > -	unsigned i = 0;
> > +	unsigned i = 0, bytes = 0;
> >   	bool bounce = false;
> > -	int sectors = 0;
> > +	int sectors;
> >   	bio_for_each_segment(from, *bio_orig, iter) {
> >   		if (i++ < BIO_MAX_VECS)
> > -			sectors += from.bv_len >> 9;
> > +			bytes += from.bv_len;
> >   		if (PageHighMem(from.bv_page))
> >   			bounce = true;
> >   	}
> >   	if (!bounce)
> >   		return;
> > +	/*
> > +	 * Individual bvecs might not be logical block aligned. Round down
> > +	 * the split size so that each bio is properly block size aligned,
> > +	 * even if we do not use the full hardware limits.
> > +	 */
> > +	sectors = ALIGN_DOWN(bytes, queue_logical_block_size(q)) >>
> > +			SECTOR_SHIFT;
> >   	if (sectors < bio_sectors(*bio_orig)) {
> >   		bio = bio_split(*bio_orig, sectors, GFP_NOIO, &bounce_bio_split);
> >   		bio_chain(bio, *bio_orig);
> 
> Do I see correctly that there are two changes in this patch: counting bytes
> instead of sectors and also splitting at logical block boundaries instead of
> a 512-byte boundary? Should this patch perhaps be split?

The code previously would only split on a bvec boundary. All bvecs were logical
block sized, so that part is not changing. We just needed to be able to split
mid-bvec since the series enables unaligned offsets to match hardware
capabilities.