linux-kernel - Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation

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Message-ID: <Z+BZOKSpyPA1Pyu+@nvidia.com>
Date: Sun, 23 Mar 2025 15:55:52 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Changyuan Lyu <changyuanl@...gle.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory
 preservation

On Sat, Mar 22, 2025 at 03:12:26PM -0400, Mike Rapoport wrote:
> This hunk actually came from me. I decided to keep it simple for now and
> check what are the alternatives, like moving away from memblock_reserve(),
> adding a maple_tree or even something else.

Okat, makes sense to me
 
> > > +		page->private = order;
> > 
> > Can't just set the page order directly? Why use private?
> 
> Setting the order means recreating the folio the way prep_compound_page()
> does. I think it's better to postpone it until the folio is requested. This
> way it might run after SMP is enabled. 

I see, that makes sense, but also it could stil use page->order..

> Besides, when we start allocating
> folios separately from struct page, initializing it here would be a real
> issue.

Yes, but also we wouldn't have page->private to make it work.. Somehow
anything we want to carry over would have to become encoded in the
memdesc directly.

I think this supports my remark someplace else that any user of this
that wants to preserve per-page data should do it on its own somehow
as an add-on-top?

Jason