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

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Message-ID: <CA+CK2bCV-UbfDb=QmyJrX3xWMToCO5b5a1R+Px5QOXafF_AqRg@mail.gmail.com>
Date: Wed, 17 Sep 2025 10:48:08 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Jason Miu <jasonmiu@...gle.com>, 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>, 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 Wed, Sep 17, 2025 at 7:36 AM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> 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.

To be fair above it is referred to as a page table *like* data
structure, but I agree kho radix tree sounds like a good overall name
for this, and it might make sense to rename from kho_page_table to
kho_radix_tree in other places.

>
> Jason