Re: [PATCH 17/29] fsdax: factor out a dax_memzero helper

Dan Williams
2021-11-23T21:22:27Z

On Tue, Nov 9, 2021 at 12:34 AM Christoph Hellwig <hch@lst.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@intel.com>

> Signed-off-by: Christoph Hellwig <hch@lst.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
>