linux-ext4 - Re: [PATCH 08/11] dm-linear: add a linear_dax

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Date:   Wed, 27 Oct 2021 18:32:58 -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 08/11] dm-linear: add a linear_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.

Looks good.

Mike, ack?

>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/md/dm-linear.c | 49 +++++++++++++-----------------------------
>  1 file changed, 15 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
> index 32fbab11bf90c..bf03f73fd0f36 100644
> --- a/drivers/md/dm-linear.c
> +++ b/drivers/md/dm-linear.c
> @@ -164,63 +164,44 @@ static int linear_iterate_devices(struct dm_target *ti,
>  }
>
>  #if IS_ENABLED(CONFIG_FS_DAX)
> +static struct dax_device *linear_dax_pgoff(struct dm_target *ti, pgoff_t *pgoff)
> +{
> +       struct linear_c *lc = ti->private;
> +       sector_t sector = linear_map_sector(ti, *pgoff << PAGE_SECTORS_SHIFT);
> +
> +       *pgoff = (get_start_sect(lc->dev->bdev) + sector) >> PAGE_SECTORS_SHIFT;
> +       return lc->dev->dax_dev;
> +}
> +
>  static long linear_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
>                 long nr_pages, void **kaddr, pfn_t *pfn)
>  {
> -       long ret;
> -       struct linear_c *lc = ti->private;
> -       struct block_device *bdev = lc->dev->bdev;
> -       struct dax_device *dax_dev = lc->dev->dax_dev;
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> -
> -       dev_sector = linear_map_sector(ti, sector);
> -       ret = bdev_dax_pgoff(bdev, dev_sector, nr_pages * PAGE_SIZE, &pgoff);
> -       if (ret)
> -               return ret;
> +       struct dax_device *dax_dev = linear_dax_pgoff(ti, &pgoff);
> +
>         return dax_direct_access(dax_dev, pgoff, nr_pages, kaddr, pfn);
>  }
>
>  static size_t linear_dax_copy_from_iter(struct dm_target *ti, pgoff_t pgoff,
>                 void *addr, size_t bytes, struct iov_iter *i)
>  {
> -       struct linear_c *lc = ti->private;
> -       struct block_device *bdev = lc->dev->bdev;
> -       struct dax_device *dax_dev = lc->dev->dax_dev;
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> +       struct dax_device *dax_dev = linear_dax_pgoff(ti, &pgoff);
>
> -       dev_sector = linear_map_sector(ti, sector);
> -       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 linear_dax_copy_to_iter(struct dm_target *ti, pgoff_t pgoff,
>                 void *addr, size_t bytes, struct iov_iter *i)
>  {
> -       struct linear_c *lc = ti->private;
> -       struct block_device *bdev = lc->dev->bdev;
> -       struct dax_device *dax_dev = lc->dev->dax_dev;
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> +       struct dax_device *dax_dev = linear_dax_pgoff(ti, &pgoff);
>
> -       dev_sector = linear_map_sector(ti, sector);
> -       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 linear_dax_zero_page_range(struct dm_target *ti, pgoff_t pgoff,
>                                       size_t nr_pages)
>  {
> -       int ret;
> -       struct linear_c *lc = ti->private;
> -       struct block_device *bdev = lc->dev->bdev;
> -       struct dax_device *dax_dev = lc->dev->dax_dev;
> -       sector_t dev_sector, sector = pgoff * PAGE_SECTORS;
> -
> -       dev_sector = linear_map_sector(ti, sector);
> -       ret = bdev_dax_pgoff(bdev, dev_sector, nr_pages << PAGE_SHIFT, &pgoff);
> -       if (ret)
> -               return ret;
> +       struct dax_device *dax_dev = linear_dax_pgoff(ti, &pgoff);
> +
>         return dax_zero_page_range(dax_dev, pgoff, nr_pages);
>  }
>
> --
> 2.30.2
>