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

["Verma, Vishal L" <vishal.l.verma@intel.com>]

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