linux-kernel - Re: [RFC v1 0/4] Make KHO Stateless

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Message-ID: <20250917113609.GB1086830@nvidia.com>
Date: Wed, 17 Sep 2025 08:36:09 -0300
From: Jason Gunthorpe <jgg@...dia.com>
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>,
	Joel Granados <joel.granados@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Mike Rapoport <rppt@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Petr Mladek <pmladek@...e.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Steven Chen <chenste@...ux.microsoft.com>,
	Yan Zhao <yan.y.zhao@...el.com>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC v1 0/4] Make KHO Stateless

On Tue, Sep 16, 2025 at 07:50:15PM -0700, Jason Miu wrote:
> This series transitions KHO from an xarray-based metadata tracking
> system with serialization to using page table like data structures
> 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 former KHO state machine by deprecating the finalize
>   and abort states.
> - Pass preservation metadata more directly to the next kernel via the FDT.
> 
> The new approach uses a per-order page table structure (kho_order_table,
> kho_page_table, kho_bitmap_table) to mark preserved pages. The physical
> address of the root `kho_order_table` is passed in the FDT, allowing the
> next kernel to reconstruct the preserved memory map.

It is not a "page table" structure, it is just a radix tree with bits
as the leaf.

Jason