You mean like submit_bio_wait() is a blocking operation?
On Mon, 7 Dec 2020 at 21:36, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Sun, Dec 06, 2020 at 01:53:30PM +0800, Tom Yan wrote:
> > At least the SCSI disk driver is "benevolent" when it try to decide
> > whether the device actually supports write zeroes, i.e. unless the
> > device explicity report otherwise, it assumes it does at first.
> >
> > Therefore before we pile up bios that would fail at the end, we try
> > the command/request once, as not doing so could trigger quite a
> > disaster in at least certain case. For example, the host controller
> > can be messed up entirely when one does `blkdiscard -z` a UAS drive.
> >
> > Signed-off-by: Tom Yan <tom.ty89@xxxxxxxxx>
> > ---
> > block/blk-lib.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > index e90614fd8d6a..c1e9388a8fb8 100644
> > --- a/block/blk-lib.c
> > +++ b/block/blk-lib.c
> > @@ -250,6 +250,7 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
> > struct bio *bio = *biop;
> > unsigned int max_write_zeroes_sectors;
> > struct request_queue *q = bdev_get_queue(bdev);
> > + int i = 0;
> >
> > if (!q)
> > return -ENXIO;
> > @@ -264,7 +265,17 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
> > return -EOPNOTSUPP;
> >
> > while (nr_sects) {
> > - bio = blk_next_bio(bio, 0, gfp_mask);
> > + if (i != 1) {
> > + bio = blk_next_bio(bio, 0, gfp_mask);
> > + } else {
> > + submit_bio_wait(bio);
> > + bio_put(bio);
> > +
> > + if (bdev_write_zeroes_sectors(bdev) == 0)
> > + return -EOPNOTSUPP;
> > + else
>
> This means you now massively slow down say nvme operations by adding
> a wait. If at all we need a maybe supports write zeroes flag and
> only do that if the driver hasn't decided yet if write zeroes is
> actually supported.
