Re: [PATCH 3/6] xfs: Don't use unwritten extents for DAX

[Jan Kara <jack@xxxxxxx>]

On Tue 03-11-15 08:44:24, Dave Chinner wrote:
> Realistically, dax_clear_blocks() should probably be implemented at
> the pmem driver layer through blkdev_issue_zeroout() because all it
> does is directly map the sector/len to pfn via bdev_direct_access()
> and then zero it - it's a sector based, block device operation. We
> don't actually need a special case path for DAX here. Optimisation
> of this operation has little to do with the filesystem.

Yep. This is actually what I did in ext4 - the block zeroing is using the
ext4 block zeroout path which ends up calling blkdev_issue_zeroout(). I
didn't want to special-case DAX and figured out that if we want
performance, we should implement blkdev_issue_zeroout() efficiently for
pmem. After all ext4 uses blkdev_issue_zeroout() in other extent conversion
cases where zeroing out is needed.

                                                                Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR