Re: [PATCH v4 16/28] cxl/region: Add sparse DAX region support

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Mon, 07 Oct 2024 18:16:22 -0500
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
> 
> 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.  Add a create_dc_region()
> sysfs entry to create such regions.  Special case DC 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.
> 
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Looks fine to me, though the DAX bit is not an area I know enough about.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>