linux-ext4 - Re: [PATCH 17/29] fsdax: factor out a dax

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Date:   Tue, 23 Nov 2021 13:22:13 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Mike Snitzer <snitzer@...hat.com>, 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 17/29] fsdax: factor out a dax_memzero helper

On Tue, Nov 9, 2021 at 12:34 AM Christoph Hellwig <hch@....de> wrote:
>
> Factor out a helper for the "manual" zeroing of a DAX range to clean
> up dax_iomap_zero a lot.
>

Small / optional fixup below:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>

> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  fs/dax.c | 36 +++++++++++++++++++-----------------
>  1 file changed, 19 insertions(+), 17 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index d7a923d152240..dc9ebeff850ab 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1121,34 +1121,36 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
>  }
>  #endif /* CONFIG_FS_DAX_PMD */
>
> +static int dax_memzero(struct dax_device *dax_dev, pgoff_t pgoff,
> +               unsigned int offset, size_t size)
> +{
> +       void *kaddr;
> +       long rc;
> +
> +       rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
> +       if (rc >= 0) {

Technically this should be "> 0" because dax_direct_access() returns
nr_available_pages @pgoff, but this isn't broken because
dax_direct_access() converts the "zero pages available" case into
-ERANGE.

> +               memset(kaddr + offset, 0, size);
> +               dax_flush(dax_dev, kaddr + offset, size);
> +       }
> +       return rc;
> +}
> +
>  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
>  {
>         pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
>         long rc, id;
> -       void *kaddr;
> -       bool page_aligned = false;
>         unsigned offset = offset_in_page(pos);
>         unsigned size = min_t(u64, PAGE_SIZE - offset, length);
>
> -       if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
> -               page_aligned = true;
> -
>         id = dax_read_lock();
> -
> -       if (page_aligned)
> +       if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
>                 rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
>         else
> -               rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> -       if (rc < 0) {
> -               dax_read_unlock(id);
> -               return rc;
> -       }
> -
> -       if (!page_aligned) {
> -               memset(kaddr + offset, 0, size);
> -               dax_flush(iomap->dax_dev, kaddr + offset, size);
> -       }
> +               rc = dax_memzero(iomap->dax_dev, pgoff, offset, size);
>         dax_read_unlock(id);
> +
> +       if (rc < 0)
> +               return rc;
>         return size;
>  }
>
> --
> 2.30.2
>