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

Keith Busch
2022-07-25T14:47:09Z

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@kernel.org>
> >
> > Individual bv_len's may not be a sector size.
> >
> > Signed-off-by: Keith Busch <kbusch@kernel.org>
> > Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> > Reviewed-by: Pankaj Raghav <p.raghav@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.