Re: [RFC PATCH 1/4] cxl/extent: Promote cxlr_dax->region_extent to an xarray

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 27 Apr 2026 10:12:02 -0500
Ira Weiny <ira.weiny@intel.com> wrote:

> Jonathan Cameron wrote:
> >   
> > > Look at the diagrams in this presentation:
> > > 
> > > https://lpc.events/event/18/contributions/1826/attachments/1435/3335/LPC2024_CXL_DCD-v2.pdf
> > > 
> > > 'DAX dev 1' covers memory from Extent A and Extent B.  What yall will want
> > > to do is ensure that the region extents which get surfaced are ordered
> > > based on the sequence number _when_ _the_ _dax_ _device_ is created.  The
> > > order they come into the host does not really matter.  Although yea the
> > > spec has a bunch of rules...  so whatever, follow those.  But it is the
> > > dax device which groups the extents into a contiguous HPA range and maps  
> > 
> > On this bit, HPA?  Why would extents be contiguous in HPA?  Contiguous
> > in the DAX device mapping sure, but not HPA.  
> 
> I'm not saying the _extents_ are contiguous in HPA.  I said they get
> _mapped_ into a contiguous HPA _by_ the DAX device.

That's not HPA at that point, it's a VA of some type.
Now maybe it smells like HPA in some DAX interface but if it does
we should think about any renames etc necessary to avoid it doing
so!  Or introduce DAXPA (not DPA for obvious reasons ;)

> 
> IOW the DAX device has some policy(tm) which looks at the extents and
> decides which ones are part of the device (the grouping I mention above).
> Then it presents a contiguous HPA to the user by mapping those
> discontinuous extents.
> 
> Ira