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

[Ira Weiny]

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.

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