[PATCH] nvme: fix handling single range discard request

[Ming Lei]

On Mon, Mar 06, 2023 at 04:21:08PM +0200, Sagi Grimberg wrote:
> 
> 
> On 3/4/23 01:13, Ming Lei wrote:
> > When investigating one customer report on warning in nvme_setup_discard,
> > we observed the controller(nvme/tcp) actually exposes
> > queue_max_discard_segments(req->q) == 1.
> > 
> > Obviously the current code can't handle this situation, since contiguity
> > merge like normal RW request is taken.
> > 
> > Fix the issue by building range from request sector/nr_sectors directly.
> > 
> > Fixes: b35ba01ea697 ("nvme: support ranged discard requests")
> > Signed-off-by: Ming Lei <ming.lei at redhat.com>
> > ---
> >   drivers/nvme/host/core.c | 28 +++++++++++++++++++---------
> >   1 file changed, 19 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > index c2730b116dc6..d4be525f8100 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -781,16 +781,26 @@ static blk_status_t nvme_setup_discard(struct nvme_ns *ns, struct request *req,
> >   		range = page_address(ns->ctrl->discard_page);
> >   	}
> > -	__rq_for_each_bio(bio, req) {
> > -		u64 slba = nvme_sect_to_lba(ns, bio->bi_iter.bi_sector);
> > -		u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
> > -
> > -		if (n < segments) {
> > -			range[n].cattr = cpu_to_le32(0);
> > -			range[n].nlb = cpu_to_le32(nlb);
> > -			range[n].slba = cpu_to_le64(slba);
> > +	if (queue_max_discard_segments(req->q) == 1) {
> > +		u64 slba = nvme_sect_to_lba(ns, blk_rq_pos(req));
> > +		u32 nlb = blk_rq_sectors(req) >> (ns->lba_shift - 9);
> > +
> > +		range[0].cattr = cpu_to_le32(0);
> > +		range[0].nlb = cpu_to_le32(nlb);
> > +		range[0].slba = cpu_to_le64(slba);
> > +		n = 1;
> > +	} else {
> > +		__rq_for_each_bio(bio, req) {
> > +			u64 slba = nvme_sect_to_lba(ns, bio->bi_iter.bi_sector);
> > +			u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
> > +
> > +			if (n < segments) {
> > +				range[n].cattr = cpu_to_le32(0);
> > +				range[n].nlb = cpu_to_le32(nlb);
> > +				range[n].slba = cpu_to_le64(slba);
> > +			}
> > +			n++;
> >   		}
> > -		n++;
> >   	}
> >   	if (WARN_ON_ONCE(n != segments)) {
> 
> 
> Maybe just set segments to min(blk_rq_nr_discard_segments(req),
> queue_max_discard_segments(req->q)) and let the existing code do
> its thing?

What is the existing code for applying min()?

For block layer merge code, it has to cover two kinds of discard merge:

- the traditional single range discard for most of devices
- multi range discard merge for nvme and virtio-blk which takes same
fix

For driver side, it has to do similar handling if both single-range and
multi-range discard are supported:

- each bio is one discard range for multi-range discard
- the whole request(may include more than 1 bios) is the single discard
range for single-range discard


Thanks, 
Ming