linux-kernel - Re: [RFC v3 2/2] pmem: enable pmem_submit

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Date:   Wed, 16 Feb 2022 09:39:09 +0100
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Linux NVDIMM <nvdimm@...ts.linux.dev>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jmoyer <jmoyer@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        Pankaj Gupta <pankaj.gupta@...os.com>
Subject: Re: [RFC v3 2/2] pmem: enable pmem_submit_bio for asynchronous flush

> >
> > Return from "pmem_submit_bio" when asynchronous flush is
> > still in progress in other context.
> >
> > Signed-off-by: Pankaj Gupta <pankaj.gupta.linux@...il.com>
> > ---
> >  drivers/nvdimm/pmem.c        | 15 ++++++++++++---
> >  drivers/nvdimm/region_devs.c |  4 +++-
> >  2 files changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index fe7ece1534e1..f20e30277a68 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -201,8 +201,12 @@ static void pmem_submit_bio(struct bio *bio)
> >         struct pmem_device *pmem = bio->bi_bdev->bd_disk->private_data;
> >         struct nd_region *nd_region = to_region(pmem);
> >
> > -       if (bio->bi_opf & REQ_PREFLUSH)
> > +       if (bio->bi_opf & REQ_PREFLUSH) {
> >                 ret = nvdimm_flush(nd_region, bio);
> > +               /* asynchronous flush completes in other context */
>
> I think a negative error code is a confusing way to capture the case
> of "bio successfully coalesced to previously pending flush request.
> Perhaps reserve negative codes for failure, 0 for synchronously
> completed, and > 0 for coalesced flush request.

Yes. I implemented this way previously, will revert it to. Thanks!

>
> > +               if (ret == -EINPROGRESS)
> > +                       return;
> > +       }
> >
> >         do_acct = blk_queue_io_stat(bio->bi_bdev->bd_disk->queue);
> >         if (do_acct)
> > @@ -222,13 +226,18 @@ static void pmem_submit_bio(struct bio *bio)
> >         if (do_acct)
> >                 bio_end_io_acct(bio, start);
> >
> > -       if (bio->bi_opf & REQ_FUA)
> > +       if (bio->bi_opf & REQ_FUA) {
> >                 ret = nvdimm_flush(nd_region, bio);
> > +               /* asynchronous flush completes in other context */
> > +               if (ret == -EINPROGRESS)
> > +                       return;
> > +       }
> >
> >         if (ret)
> >                 bio->bi_status = errno_to_blk_status(ret);
> >
> > -       bio_endio(bio);
> > +       if (bio)
> > +               bio_endio(bio);
> >  }
> >
> >  static int pmem_rw_page(struct block_device *bdev, sector_t sector,
> > diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> > index 9ccf3d608799..8512d2eaed4e 100644
> > --- a/drivers/nvdimm/region_devs.c
> > +++ b/drivers/nvdimm/region_devs.c
> > @@ -1190,7 +1190,9 @@ int nvdimm_flush(struct nd_region *nd_region, struct bio *bio)
> >         if (!nd_region->flush)
> >                 rc = generic_nvdimm_flush(nd_region);
> >         else {
> > -               if (nd_region->flush(nd_region, bio))
> > +               rc = nd_region->flush(nd_region, bio);
> > +               /* ongoing flush in other context */
> > +               if (rc && rc != -EINPROGRESS)
> >                         rc = -EIO;
>
> Why change this to -EIO vs just let the error code through untranslated?

The reason was to be generic error code instead of returning host side
return codes to guest?

Thanks!
Pankaj
>
> >         }
> >
> > --
> > 2.25.1
> >
> >