linux-kernel - Re: [PATCH v3 06/10] fsdax: Add dax_iomap_cow_copy() for dax_iomap

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Date:   Thu, 1 Apr 2021 12:15:06 +0530
From:   Ritesh Harjani <ritesh.list@...il.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        willy@...radead.org, jack@...e.cz, viro@...iv.linux.org.uk,
        linux-btrfs@...r.kernel.org, ocfs2-devel@....oracle.com,
        david@...morbit.com, hch@....de, rgoldwyn@...e.de
Subject: Re: [PATCH v3 06/10] fsdax: Add dax_iomap_cow_copy() for
 dax_iomap_zero

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@...itsu.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@...il.com>