On Wed, Feb 03, 2021 at 10:35:17AM +0800, Ming Lei wrote:
>
> On Tue, Feb 02, 2021 at 03:43:55PM -0500, David Jeffery wrote:
> > The return 0 does seem to be an old relic that does not make sense anymore.
> > Moving REQ_OP_SECURE_ERASE to be with discard and removing the old return 0,
> > is this what you had in mind?
> >
> >
> > diff --git a/block/blk-merge.c b/block/blk-merge.c
> > index 808768f6b174..68458aa01b05 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -383,8 +383,14 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
> > switch (bio_op(rq->bio)) {
> > case REQ_OP_DISCARD:
> > case REQ_OP_SECURE_ERASE:
> > + if (queue_max_discard_segments(rq->q) > 1) {
> > + struct bio *bio = rq->bio;
> > + for_each_bio(bio)
> > + nr_phys_segs++;
> > + return nr_phys_segs;
> > + }
> > + /* fall through */
> > case REQ_OP_WRITE_ZEROES:
> > - return 0;
> > case REQ_OP_WRITE_SAME:
> > return 1;
>
> WRITE_SAME uses same buffer, so the nr_segment is still one; WRITE_ZERO
> doesn't need extra payload, so nr_segments is zero, see
> blk_bio_write_zeroes_split(), blk_bio_write_same_split, attempt_merge()
> and blk_rq_merge_ok().
>
I thought you mentioned virtio-blk because of how some drivers handle
zeroing and discarding similarly and wanted to align the segment count with
discard behavior for WRITE_ZEROES too. (Though that would also need an update
to blk_bio_write_zeroes_split as you pointed out.) So you want me to leave
WRITE_ZEROES behavior alone and let blk_rq_nr_discard_segments() keep doing
the hiding of a 0 rq->nr_phys_segments as 1 segment in the WRITE_ZEROES treated
as a discard case?
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 808768f6b174..756473295f19 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -383,6 +383,14 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
switch (bio_op(rq->bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
+ if (queue_max_discard_segments(rq->q) > 1) {
+ struct bio *bio = rq->bio;
+
+ for_each_bio(bio)
+ nr_phys_segs++;
+ return nr_phys_segs;
+ }
+ return 1;
case REQ_OP_WRITE_ZEROES:
return 0;
case REQ_OP_WRITE_SAME:
--
David Jeffery
