Re: [PATCH 01/15] dax: export a low-level __dax_zero_page_range helper

Verma, Vishal L
2016-05-11T22:43:32Z

On Mon, 2016-05-09 at 10:47 +0200, Christoph Hellwig wrote:
> This allows XFS to perform zeroing using the iomap infrastructure and
> avoid buffer heads.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/dax.c            | 35 ++++++++++++++++++++---------------
>  include/linux/dax.h |  7 +++++++
>  2 files changed, 27 insertions(+), 15 deletions(-)

This looks good to me.

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

>
> diff --git a/fs/dax.c b/fs/dax.c
> index 90322eb..6d5d744 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1082,6 +1082,23 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma,
> struct vm_fault *vmf)
>  }
>  EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
>
> +int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
> + unsigned int offset, unsigned int length)
> +{
> + struct blk_dax_ctl dax = {
> + .sector = sector,
> + .size = PAGE_CACHE_SIZE,
> + };
> +
> + if (dax_map_atomic(bdev, &dax) < 0)
> + return PTR_ERR(dax.addr);
> + clear_pmem(dax.addr + offset, length);
> + wmb_pmem();
> + dax_unmap_atomic(bdev, &dax);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(__dax_zero_page_range);
> +
>  /**
>   * dax_zero_page_range - zero a range within a page of a DAX file
>   * @inode: The file being truncated
> @@ -1117,23 +1134,11 @@ int dax_zero_page_range(struct inode *inode,
> loff_t from, unsigned length,
>   bh.b_bdev = inode->i_sb->s_bdev;
>   bh.b_size = PAGE_CACHE_SIZE;
>   err = get_block(inode, index, &bh, 0);
> - if (err < 0)
> + if (err < 0 || !buffer_written(&bh))
>   return err;
> - if (buffer_written(&bh)) {
> - struct block_device *bdev = bh.b_bdev;
> - struct blk_dax_ctl dax = {
> - .sector = to_sector(&bh, inode),
> - .size = PAGE_CACHE_SIZE,
> - };
>
> - if (dax_map_atomic(bdev, &dax) < 0)
> - return PTR_ERR(dax.addr);
> - clear_pmem(dax.addr + offset, length);
> - wmb_pmem();
> - dax_unmap_atomic(bdev, &dax);
> - }
> -
> - return 0;
> + return __dax_zero_page_range(bh.b_bdev, to_sector(&bh,
> inode),
> + offset, length);
>  }
>  EXPORT_SYMBOL_GPL(dax_zero_page_range);
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 636dd59..8155b81 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -17,12 +17,19 @@ int __dax_fault(struct vm_area_struct *, struct
> vm_fault *, get_block_t,
>
>  #ifdef CONFIG_FS_DAX
>  struct page *read_dax_sector(struct block_device *bdev, sector_t n);
> +int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
> + unsigned int offset, unsigned int length);
>  #else
>  static inline struct page *read_dax_sector(struct block_device *bdev,
>   sector_t n)
>  {
>   return ERR_PTR(-ENXIO);
>  }
> +static inline int __dax_zero_page_range(struct block_device *bdev,
> + sector_t sector, unsigned int offset, unsigned int
> length)
> +{
> + return -ENXIO;
> +}
>  #endif
>
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE