linux-rng/include/linux/kho_radix_tree.h, branch master

kho: add kho_radix_init_tree()

2026-08-04T06:22:36Z

Move the initialization logic of the radix tree into kho_radix_init_tree() instead of having users open-code it. Makes the boundaries cleaner and reduces code duplication when a new user of the radix tree will be added in a future commit. Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-13-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: allow destroying KHO radix tree

2026-08-04T06:20:32Z

Add kho_radix_destroy_tree() which allows destroying the radix tree and freeing all its pages. This is will be used by the upcoming scratch extension mechanism. It creates a radix tree to track free blocks and then frees them after telling memblock about them. Reviewed-by: Pasha Tatashin Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-12-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: add data argument to radix walk callback

2026-08-04T06:19:50Z

Add an opaque data pointer argument to kho_radix_walk_cb_t. This can be used by callers to pass extra information to the callback. Reviewed-by: Pasha Tatashin Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-10-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: add callback for table pages

2026-08-04T06:19:28Z

The KHO memory preservation radix tree does not mark the table pages themselves as preserved. This is done to avoid a circular dependency where preserving a page can lead of allocating other preserved pages. This means any walker looking for free ranges of memory outside of scratch areas will ignore the table Add a table callback that is invoked for each table page. The callback is given the physical address of the table page. This is useful for the upcoming mechanism that discovers blocks of memory with no preserved pages and lets them be used for boot memory. Another use case is for users of the radix tree other than KHO itself. The radix tree does not preserve its own pages due to the circular dependency described above. But external users of the radix tree would need to preserve and restore their pages for the radix tree to survive past early boot. They can use this callback to do so. Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-9-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: add a struct for radix callbacks

2026-08-04T06:19:07Z

A future commit will add more callbacks for the KHO radix tree. Add a struct for collecting the callbacks. Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-8-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: generalize radix tree APIs

2026-08-03T18:53:54Z

The KHO radix tree is a data structure that can track the presence or absence of an arbitrary key, with nothing inherently tied to KHO memory preservation tracking. This was one of the design goals of the radix tree. This was done to enable it to be re-used by other users of KHO. Despite that, the radix tree APIs are very closely tied to KHO memory preservation tracking. Adding a key is done by kho_radix_add_page(), which encodes it as a page tracking operation and takes in PFN and order. kho_radix_del_page() does the same. These functions encode the key internally that goes into the radix tree. kho_radix_walk_tree() does the same by baking the PFN and order into the callback arguments. Generalize the APIs by taking the key directly and doing the encoding at the callers. Rename the functions to kho_radix_add_key() and kho_radix_del_key(). In practice, this removes a line each from the functions and moves the encoding function call to the callers. Similarly, update kho_radix_tree_walk_callback_t to take the key directly. Now that key encoding is no longer an inherent part of the radix tree and can be decided by the user, rename kho_radix_{encode,decode}_key() to kho_{encode,decode}_radix_key(). This moves them out of the "kho_radix_" name space into the "kho_" namespace. This emphasizes that this is KHO's way of encoding the key for its radix tree. Reviewed-by: Pasha Tatashin Signed-off-by: Pratyush Yadav (Google) Link: https://patch.msgid.link/20260801084833.1897543-2-pratyush@kernel.org Signed-off-by: Mike Rapoport (Microsoft)

kho: adopt radix tree for preserved memory tracking

2026-04-05T20:53:04Z

Patch series "Make KHO Stateless", v9. This series transitions KHO from an xarray-based metadata tracking system with serialization to a radix tree data structure that can be passed directly to the next kernel. The key motivations for this change are to: - Eliminate the need for data serialization before kexec. - Remove the KHO finalize state. - Pass preservation metadata more directly to the next kernel via the FDT. The new approach uses a radix tree to mark preserved pages. A page's physical address and its order are encoded into a single value. The tree is composed of multiple levels of page-sized tables, with leaf nodes being bitmaps where each set bit represents a preserved page. The physical address of the radix tree's root is passed in the FDT, allowing the next kernel to reconstruct the preserved memory map. This series is broken down into the following patches: 1. kho: Adopt radix tree for preserved memory tracking: Replaces the xarray-based tracker with the new radix tree implementation and increments the ABI version. 2. kho: Remove finalize state and clients: Removes the now-obsolete kho_finalize() function and its usage from client code and debugfs. This patch (of 2): 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. [ran.xiaokai@zte.com.cn: fix child node parsing for debugfs in/sub_fdts] Link: https://lkml.kernel.org/r/20260309033530.244508-1-ranxiaokai627@163.com Link: https://lkml.kernel.org/r/20260206021428.3386442-1-jasonmiu@google.com Link: https://lkml.kernel.org/r/20260206021428.3386442-2-jasonmiu@google.com Signed-off-by: Jason Miu Signed-off-by: Ran Xiaokai Reviewed-by: Pasha Tatashin Reviewed-by: Mike Rapoport (Microsoft) Cc: Alexander Graf Cc: Baoquan He Cc: Changyuan Lyu Cc: David Matlack Cc: David Rientjes Cc: Jason Gunthorpe Cc: Pratyush Yadav Cc: Ran Xiaokai Signed-off-by: Andrew Morton