Re: [RFC v3 2/2] pmem: enable pmem_submit_bio for asynchronous flush

From: Dan Williams <dan.j.williams@intel.com>
To: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Linux NVDIMM <nvdimm@lists.linux.dev>,
	virtualization@lists.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	jmoyer <jmoyer@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Vishal L Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	"Weiny, Ira" <ira.weiny@intel.com>,
	Pankaj Gupta <pankaj.gupta@ionos.com>
Subject: Re: [RFC v3 2/2] pmem: enable pmem_submit_bio for asynchronous flush
Date: Tue, 15 Feb 2022 19:34:24 -0800	[thread overview]
Message-ID: <CAPcyv4gM99M8Waw9uEZefvpK0BsTkjGznLxUOMcMkGpk6SuHyA@mail.gmail.com> (raw)
In-Reply-To: <20220111161937.56272-3-pankaj.gupta.linux@gmail.com>

On Tue, Jan 11, 2022 at 8:21 AM Pankaj Gupta
<pankaj.gupta.linux@gmail.com> wrote:
>
> Return from "pmem_submit_bio" when asynchronous flush is
> still in progress in other context.
>
> Signed-off-by: Pankaj Gupta <pankaj.gupta.linux@gmail.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.

> +               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?

>         }
>
> --
> 2.25.1
>
>