Re: [PATCH v9 1/2] kho: Adopt radix tree for preserved memory tracking

[Mike Rapoport <rppt@kernel.org>]

On Thu, Feb 05, 2026 at 06:14:27PM -0800, Jason Miu wrote:
> Introduce a radix tree implementation for tracking preserved memory
> pages and switch the KHO memory tracking mechanism to use it. This
> lays the groundwork for a stateless KHO implementation that eliminates
> the need for serialization and the associated "finalize" state.
> 
> This patch introduces the core radix tree data structures and
> constants to the KHO ABI. It adds the radix tree node and leaf
> structures, along with documentation for the radix tree key encoding
> scheme that combines a page's physical address and order.
> 
> To support broader use by other kernel subsystems, such as hugetlb
> preservation, the core radix tree manipulation functions are exported
> as a public API.
> 
> The xarray-based memory tracking is replaced with this new radix tree
> implementation. The core KHO preservation and unpreservation functions
> are wired up to use the radix tree helpers. On boot, the second kernel
> restores the preserved memory map by walking the radix tree whose root
> physical address is passed via the FDT.
> 
> The ABI `compatible` version is bumped to "kho-v2" to reflect the
> structural changes in the preserved memory map and sub-FDT property
> names. This includes renaming "fdt" to "preserved-data" to better
> reflect that preserved state may use formats other than FDT.
> 
> Signed-off-by: Jason Miu <jasonmiu@google.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.