linux-ext4 - Re: [PATCH 10/11] dm-stripe: add a stripe_dax

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Date:   Wed, 27 Oct 2021 18:41:13 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>, Mike Snitzer <snitzer@...hat.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        device-mapper development <dm-devel@...hat.com>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-erofs@...ts.ozlabs.org,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 10/11] dm-stripe: add a stripe_dax_pgoff helper

On Sun, Oct 17, 2021 at 9:41 PM Christoph Hellwig <hch@....de> wrote:
>
> Add a helper to perform the entire remapping for DAX accesses.  This
> helper open codes bdev_dax_pgoff given that the alignment checks have
> already been done by the submitting file system and don't need to be
> repeated.

Again, looks good. Kind of embarrassing when the open-coded version is
less LOC than using the helper.

Mike, ack?

>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/md/dm-stripe.c | 63 ++++++++++--------------------------------
>  1 file changed, 15 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
> index f084607220293..50dba3f39274c 100644
> --- a/drivers/md/dm-stripe.c
> +++ b/drivers/md/dm-stripe.c
> @@ -301,83 +301,50 @@ static int stripe_map(struct dm_target *ti, struct bio *bio)
>  }
>
>  #if IS_ENABLED(CONFIG_FS_DAX)
> -static long stripe_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
> -               long nr_pages, void **kaddr, pfn_t *pfn)
> +static struct dax_device *stripe_dax_pgoff(struct dm_target *ti, pgoff_t *pgoff)
>  {
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
>         struct stripe_c *sc = ti->private;
> -       struct dax_device *dax_dev;
>         struct block_device *bdev;
> +       sector_t dev_sector;
>         uint32_t stripe;
> -       long ret;
>
> -       stripe_map_sector(sc, sector, &stripe, &dev_sector);
> +       stripe_map_sector(sc, *pgoff * PAGE_SECTORS, &stripe, &dev_sector);
>         dev_sector += sc->stripe[stripe].physical_start;
> -       dax_dev = sc->stripe[stripe].dev->dax_dev;
>         bdev = sc->stripe[stripe].dev->bdev;
>
> -       ret = bdev_dax_pgoff(bdev, dev_sector, nr_pages * PAGE_SIZE, &pgoff);
> -       if (ret)
> -               return ret;
> +       *pgoff = (get_start_sect(bdev) + dev_sector) >> PAGE_SECTORS_SHIFT;
> +       return sc->stripe[stripe].dev->dax_dev;
> +}
> +
> +static long stripe_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
> +               long nr_pages, void **kaddr, pfn_t *pfn)
> +{
> +       struct dax_device *dax_dev = stripe_dax_pgoff(ti, &pgoff);
> +
>         return dax_direct_access(dax_dev, pgoff, nr_pages, kaddr, pfn);
>  }
>
>  static size_t stripe_dax_copy_from_iter(struct dm_target *ti, pgoff_t pgoff,
>                 void *addr, size_t bytes, struct iov_iter *i)
>  {
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> -       struct stripe_c *sc = ti->private;
> -       struct dax_device *dax_dev;
> -       struct block_device *bdev;
> -       uint32_t stripe;
> -
> -       stripe_map_sector(sc, sector, &stripe, &dev_sector);
> -       dev_sector += sc->stripe[stripe].physical_start;
> -       dax_dev = sc->stripe[stripe].dev->dax_dev;
> -       bdev = sc->stripe[stripe].dev->bdev;
> +       struct dax_device *dax_dev = stripe_dax_pgoff(ti, &pgoff);
>
> -       if (bdev_dax_pgoff(bdev, dev_sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
> -               return 0;
>         return dax_copy_from_iter(dax_dev, pgoff, addr, bytes, i);
>  }
>
>  static size_t stripe_dax_copy_to_iter(struct dm_target *ti, pgoff_t pgoff,
>                 void *addr, size_t bytes, struct iov_iter *i)
>  {
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> -       struct stripe_c *sc = ti->private;
> -       struct dax_device *dax_dev;
> -       struct block_device *bdev;
> -       uint32_t stripe;
> -
> -       stripe_map_sector(sc, sector, &stripe, &dev_sector);
> -       dev_sector += sc->stripe[stripe].physical_start;
> -       dax_dev = sc->stripe[stripe].dev->dax_dev;
> -       bdev = sc->stripe[stripe].dev->bdev;
> +       struct dax_device *dax_dev = stripe_dax_pgoff(ti, &pgoff);
>
> -       if (bdev_dax_pgoff(bdev, dev_sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
> -               return 0;
>         return dax_copy_to_iter(dax_dev, pgoff, addr, bytes, i);
>  }
>
>  static int stripe_dax_zero_page_range(struct dm_target *ti, pgoff_t pgoff,
>                                       size_t nr_pages)
>  {
> -       int ret;
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> -       struct stripe_c *sc = ti->private;
> -       struct dax_device *dax_dev;
> -       struct block_device *bdev;
> -       uint32_t stripe;
> +       struct dax_device *dax_dev = stripe_dax_pgoff(ti, &pgoff);
>
> -       stripe_map_sector(sc, sector, &stripe, &dev_sector);
> -       dev_sector += sc->stripe[stripe].physical_start;
> -       dax_dev = sc->stripe[stripe].dev->dax_dev;
> -       bdev = sc->stripe[stripe].dev->bdev;
> -
> -       ret = bdev_dax_pgoff(bdev, dev_sector, nr_pages << PAGE_SHIFT, &pgoff);
> -       if (ret)
> -               return ret;
>         return dax_zero_page_range(dax_dev, pgoff, nr_pages);
>  }
>
> --
> 2.30.2
>