Re: [PATCH v13 10/12] famfs: Add runtime operation-permission (opts) framework

[Gregory Price]

On Sat, Aug 22, 2026 at 10:40:29AM -0700, Darrick J. Wong wrote:
> 
> A bigger question I just thought of is sharing cxlmem between files (aka
> reflink).  Is that allowed?  I could see a theoretical usecase for
> programs A and B wanting to share some cxlmem for communication or
> heartbeats whilst having their own /a and /b files for their private
> memory.  Probably you'd just create a /common file to do that and not
> map the same cxlmem page into /a and /b, right?
> 

If the underlying memory hardware is hardware-coherent, then this would
be supportable because the coherence domains of all the hosts connected
to the large pool would extend to one another.

In our current world, these huge-memory distributed memory systems are
non-coherent and each host's coherence domain stops more or less at the
head it uses to connect to the shared media (it's probably more accurate
to say it's "device dependant" but that's besides the point).

Anyway, there's "allowed" and "useful".  You could technically do it
(maybe not with FAMFS' current guard rails) - but it would be useless
unless Process A and Process B were in the same coherence domain.

~Gregory