Re: [PATCH v9 07/19] cxl/region: Add sparse DAX region support

[Jonathan Cameron]

On Sun, 13 Apr 2025 17:52:15 -0500
Ira Weiny <ira.weiny@xxxxxxxxx> wrote:

> Dynamic Capacity CXL regions must allow memory to be added or removed
> dynamically.  In addition to the quantity of memory available the
> location of the memory within a DC partition is dynamic based on the
> extents offered by a device.  CXL DAX regions must accommodate the
> sparseness of this memory in the management of DAX regions and devices.
> 
> Introduce the concept of a sparse DAX region.  Introduce
> create_dynamic_ram_a_region() sysfs entry to create such regions.
> Special case dynamic capable regions to create a 0 sized seed DAX device
> to maintain compatibility which requires a default DAX device to hold a
> region reference.
> 
> Indicate 0 byte available capacity until such time that capacity is
> added.
> 
> Sparse regions complicate the range mapping of dax devices.  There is no
> known use case for range mapping on sparse regions.  Avoid the
> complication by preventing range mapping of dax devices on sparse
> regions.
> 
> Interleaving is deferred for now.  Add checks.
> 
> Based on an original patch by Navneet Singh.
> 
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
I'm not that familiar with the DAX parts but looks fine to me.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>