Re: [PATCH v2 2/2] dax: move writeback calls into the filesystems

[Dave Chinner <david@fromorbit.com>]

On Wed, Feb 10, 2016 at 01:48:56PM -0700, Ross Zwisler wrote:
> Previously calls to dax_writeback_mapping_range() for all DAX filesystems
> (ext2, ext4 & xfs) were centralized in filemap_write_and_wait_range().
> dax_writeback_mapping_range() needs a struct block_device, and it used to
> get that from inode->i_sb->s_bdev.  This is correct for normal inodes
> mounted on ext2, ext4 and XFS filesystems, but is incorrect for DAX raw
> block devices and for XFS real-time files.
> 
> Instead, call dax_writeback_mapping_range() directly from the filesystem
> ->writepages function so that it can supply us with a valid block
> device. This also fixes DAX code to properly flush caches in response to
> sync(2).
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/block_dev.c      | 16 +++++++++++++++-
>  fs/dax.c            | 13 ++++++++-----
>  fs/ext2/inode.c     | 11 +++++++++++
>  fs/ext4/inode.c     |  7 +++++++
>  fs/xfs/xfs_aops.c   |  9 +++++++++
>  include/linux/dax.h |  6 ++++--
>  mm/filemap.c        | 12 ++++--------
>  7 files changed, 58 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 39b3a17..fc01e43 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1693,13 +1693,27 @@ static int blkdev_releasepage(struct page *page, gfp_t wait)
>  	return try_to_free_buffers(page);
>  }
>  
> +static int blkdev_writepages(struct address_space *mapping,
> +			     struct writeback_control *wbc)
> +{
> +	if (dax_mapping(mapping)) {
> +		struct block_device *bdev = I_BDEV(mapping->host);
> +		int error;
> +
> +		error = dax_writeback_mapping_range(mapping, bdev, wbc);
> +		if (error)
> +			return error;
> +	}
> +	return generic_writepages(mapping, wbc);
> +}

Can you remind of the reason for calling generic_writepages() on DAX
enabled address spaces?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com