Re: [PATCH v9 7/8] xfs: support CoW in fsdax mode

[Christoph Hellwig]

On Fri, Sep 17, 2021 at 08:33:04AM -0700, Darrick J. Wong wrote:
> > More importantly before we can merge this series we also need the VM
> > level support for reflink-aware reverse mapping.  So while this series
> > here is no in a good enough shape I don't see how we could merge it
> > without that other series as we'd have to disallow mmap for reflink+dax
> > files otherwise.
> 
> I've forgotten why we need mm level reverse mapping again?  The pmem
> poison stuff can use ->media_failure (or whatever it was called,
> memory_failure?) to find all the owners and notify them.  Was there
> some other accounting reason that fell out of my brain?
> 
> I'm more afraid of 'sharing pages between files needs mm support'
> sparking another multi-year folioesque fight with the mm people.

Because of the way page->mapping is used by DAX.  But I think this is
mostly under control in the other series.