On Tue 25-07-17 10:01:58, Christoph Hellwig wrote: > On Tue, Jul 25, 2017 at 01:14:00AM +0300, Kirill A. Shutemov wrote: > > I guess it's up to filesystem if it wants to reuse the same spot to write > > data or not. I think your assumptions works for ext4 and xfs. I wouldn't > > be that sure for btrfs or other filesystems with CoW support. > > Or XFS with reflinks for that matter. Which currently can't be > combined with DAX, but I had a somewhat working version a few month > ago. But in cases like COW when the block mapping changes, the process must run unmap_mapping_range() before installing the new PTE so that all processes mapping this file offset actually refault and see the new mapping. So this would go through pte_none() case. Am I missing something? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
