linux-kernel - Re: [PATCH v7 0/2] Make KHO Stateless

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Message-ID: <aW57Pn4gj8lHoOO3@kernel.org>
Date: Mon, 19 Jan 2026 20:43:10 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Jason Miu <jasonmiu@...gle.com>
Cc: Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Changyuan Lyu <changyuanl@...gle.com>,
	David Matlack <dmatlack@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Pratyush Yadav <pratyush@...nel.org>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v7 0/2] Make KHO Stateless

Hi Jason,

On Thu, Jan 15, 2026 at 07:44:30PM -0800, Jason Miu wrote:
> 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.
> 
> ---
> 
> Changelog since v6 [1]:
> - Fixed a potential dangling pointer in kho_radix_add_page() on allocation failure
> - Fixed a premature return in __kho_radix_walk_tree()
> - Corrected the size type in kho_preserved_memory_reserve() to match memblock_reserve()

git range-diff claims that v5, v6 and v7 are identical.

Can you please verify that it's the latest version you intended to send?
 
> [1] https://lore.kernel.org/lkml/20260115230047.1220580-1-jasonmiu@google.com/
> 
> ---
> 
> Jason Miu (2):
>   kho: Adopt radix tree for preserved memory tracking
>   kho: Remove finalize state and clients
> 
>  Documentation/admin-guide/mm/kho.rst        |  53 +-
>  Documentation/core-api/kho/abi.rst          |   6 +
>  Documentation/core-api/kho/index.rst        |  18 +-
>  include/linux/kho/abi/kexec_handover.h      | 144 +++-
>  include/linux/kho_radix_tree.h              |  70 ++
>  kernel/liveupdate/kexec_handover.c          | 695 ++++++++++----------
>  kernel/liveupdate/kexec_handover_debugfs.c  |  23 -
>  kernel/liveupdate/kexec_handover_internal.h |   3 -
>  kernel/liveupdate/luo_core.c                |  12 +-
>  kernel/liveupdate/luo_flb.c                 |   2 +-
>  tools/testing/selftests/kho/init.c          |  20 -
>  11 files changed, 573 insertions(+), 473 deletions(-)
>  create mode 100644 include/linux/kho_radix_tree.h
> 
> 
> base-commit: 9b7977f9e39b7768c70c2aa497f04e7569fd3e00
> -- 
> 2.52.0.457.g6b5491de43-goog
> 

-- 
Sincerely yours,
Mike.