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

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Message-ID: <Z+G7iHUdRZGv1Ose@nvidia.com>
Date: Mon, 24 Mar 2025 17:07:36 -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 Mon, Mar 24, 2025 at 02:18:34PM -0400, Mike Rapoport wrote:
> On Sun, Mar 23, 2025 at 03:55:52PM -0300, Jason Gunthorpe wrote:
> > On Sat, Mar 22, 2025 at 03:12:26PM -0400, Mike Rapoport wrote:
> >  
> > > > > +		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..
> 
> But there's no page->order :)

I mean this:

static inline unsigned int folio_order(const struct folio *folio)
{
        if (!folio_test_large(folio))
                return 0;
        return folio->_flags_1 & 0xff;
}
 
> > 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.
> 
> This is a problem to solve in 2026 :)

Yes :)

Jason