Re: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite()

Jan Kara
2017-07-25T09:35:13Z

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@suse.com>
SUSE Labs, CR