>
> Add a dax operation zero_page_range, to zero a page. This will also clear any
> known poison in the page being zeroed.
>
> As of now, zeroing of one page is allowed in a single call. There
> are no callers which are trying to zero more than a page in a single call.
> Once we grow the callers which zero more than a page in single call, we
> can add that support. Primary reason for not doing that yet is that this
> will add little complexity in dm implementation where a range might be
> spanning multiple underlying targets and one will have to split the range
> into multiple sub ranges and call zero_page_range() on individual targets.
>
> Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> drivers/dax/super.c | 20 ++++++++++++++++++++
> drivers/nvdimm/pmem.c | 11 +++++++++++
> include/linux/dax.h | 4 ++++
> 3 files changed, 35 insertions(+)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 0aa4b6bc5101..e498daf3c0d7 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -344,6 +344,26 @@ size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> }
> EXPORT_SYMBOL_GPL(dax_copy_to_iter);
>
> +int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> + size_t nr_pages)
> +{
> + if (!dax_alive(dax_dev))
> + return -ENXIO;
> +
> + if (!dax_dev->ops->zero_page_range)
> + return -EOPNOTSUPP;
> + /*
> + * There are no callers that want to zero more than one page as of now.
> + * Once users are there, this check can be removed after the
> + * device mapper code has been updated to split ranges across targets.
> + */
> + if (nr_pages != 1)
> + return -EIO;
> +
> + return dax_dev->ops->zero_page_range(dax_dev, pgoff, nr_pages);
> +}
> +EXPORT_SYMBOL_GPL(dax_zero_page_range);
> +
> #ifdef CONFIG_ARCH_HAS_PMEM_API
> void arch_wb_cache_pmem(void *addr, size_t size);
> void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 075b11682192..5b774ddd0efb 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -282,6 +282,16 @@ static const struct block_device_operations pmem_fops = {
> .revalidate_disk = nvdimm_revalidate_disk,
> };
>
> +static int pmem_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> + size_t nr_pages)
> +{
> + struct pmem_device *pmem = dax_get_private(dax_dev);
> +
> + return blk_status_to_errno(pmem_do_write(pmem, ZERO_PAGE(0), 0,
> + PFN_PHYS(pgoff) >> SECTOR_SHIFT,
> + PAGE_SIZE));
> +}
> +
> static long pmem_dax_direct_access(struct dax_device *dax_dev,
> pgoff_t pgoff, long nr_pages, void **kaddr, pfn_t *pfn)
> {
> @@ -313,6 +323,7 @@ static const struct dax_operations pmem_dax_ops = {
> .dax_supported = generic_fsdax_supported,
> .copy_from_iter = pmem_copy_from_iter,
> .copy_to_iter = pmem_copy_to_iter,
> + .zero_page_range = pmem_dax_zero_page_range,
> };
>
> static const struct attribute_group *pmem_attribute_groups[] = {
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 328c2dbb4409..71735c430c05 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -34,6 +34,8 @@ struct dax_operations {
> /* copy_to_iter: required operation for fs-dax direct-i/o */
> size_t (*copy_to_iter)(struct dax_device *, pgoff_t, void *, size_t,
> struct iov_iter *);
> + /* zero_page_range: required operation. Zero page range */
> + int (*zero_page_range)(struct dax_device *, pgoff_t, size_t);
> };
>
> extern struct attribute_group dax_attribute_group;
> @@ -199,6 +201,8 @@ size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> size_t bytes, struct iov_iter *i);
> size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> size_t bytes, struct iov_iter *i);
> +int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
> + size_t nr_pages);
> void dax_flush(struct dax_device *dax_dev, void *addr, size_t size);
>
> ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
> --
> 2.20.1
Zeroing single page seems right approach for now.
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
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