Re: [PATCH v3 06/10] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

Ritesh Harjani
2021-04-01T06:45:44Z

On 21/03/19 09:52AM, Shiyang Ruan wrote:
> Punch hole on a reflinked file needs dax_copy_edge() too. Otherwise,
> data in not aligned area will be not correct. So, add the srcmap to
> dax_iomap_zero() and replace memset() as dax_copy_edge().
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> ---
> fs/dax.c | 9 +++++++--
> fs/iomap/buffered-io.c | 2 +-
> include/linux/dax.h | 3 ++-
> 3 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index cfe513eb111e..348297b38f76 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1174,7 +1174,8 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
> }
> #endif /* CONFIG_FS_DAX_PMD */
>
> -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> + struct iomap *srcmap)

Do we know why does dax_iomap_zero() operates on PAGE_SIZE range?
IIUC, dax_zero_page_range() can take nr_pages as a parameter. But we still
always use one page at a time. Why is that?

> {
> sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> pgoff_t pgoff;
> @@ -1204,7 +1205,11 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> }
>
> if (!page_aligned) {
> - memset(kaddr + offset, 0, size);
> + if (iomap->addr != srcmap->addr)
> + dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> + kaddr, true);
> + else
> + memset(kaddr + offset, 0, size);
> dax_flush(iomap->dax_dev, kaddr + offset, size);
> }
> dax_read_unlock(id);
>

Maybe the above could be simplified to this?

if (page_aligned) {
rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
} else {
rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
if (iomap->addr != srcmap->addr)
dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
kaddr, true);
else
memset(kaddr + offset, 0, size);
dax_flush(iomap->dax_dev, kaddr + offset, size);
}

dax_read_unlock(id);
return rc < 0 ? rc : size;

Other than that looks good.
Feel free to add.
Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>