linux-kernel - Re: [PATCH v4 1/2] kho: Adopt radix tree for preserved memory tracking

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Message-ID: <aWZaqcStRAK6VWLy@kernel.org>
Date: Tue, 13 Jan 2026 16:46:01 +0200
From: Mike Rapoport <rppt@...nel.org>
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>,
	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 v4 1/2] kho: Adopt radix tree for preserved memory
 tracking

On Tue, Jan 13, 2026 at 09:05:26AM -0400, Jason Gunthorpe wrote:
> On Tue, Jan 13, 2026 at 01:34:42PM +0200, Mike Rapoport wrote:
> 
> > For example mshv intends to use kho_radix_tree to track the hypervisor
> > memory and there unpreserving will be a part of the normal flow.
> 
> I do not think this is a good idea.

Sorry I wasn't clear, mshv is not going to use KHO memory tracker but
another instance of kho_radix_tree data structure. 
I don't see a problem with that.
 
> Nothing should be touching KHO until a kexec sequence is started. KHO
> calls should WARN_ON prior to this point. If a kexec sequence aborts
> then the entire radix tree should be discarded and it should go back
> to WARN_ON'ing KHO calls.

The whole point of making KHO stateless was to decouple it from kexec
sequence and let userspace control when preservation happens and to allow
preserving as much as possible ahead of time to save cycles at
kexec-reboot.

> Jason

-- 
Sincerely yours,
Mike.