linux-kernel - Re: [PATCH v3 29/30] luo: allow preserving memfd

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Message-ID: <aLABxkpPcbxyv6m_@kernel.org>
Date: Thu, 28 Aug 2025 10:14:14 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Pasha Tatashin <pasha.tatashin@...een.com>, pratyush@...nel.org,
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Subject: Re: [PATCH v3 29/30] luo: allow preserving memfd

On Tue, Aug 26, 2025 at 01:20:19PM -0300, Jason Gunthorpe wrote:
> On Thu, Aug 07, 2025 at 01:44:35AM +0000, Pasha Tatashin wrote:
> 
> > +	err = fdt_property_placeholder(fdt, "folios", preserved_size,
> > +				       (void **)&preserved_folios);
> > +	if (err) {
> > +		pr_err("Failed to reserve folios property in FDT: %s\n",
> > +		       fdt_strerror(err));
> > +		err = -ENOMEM;
> > +		goto err_free_fdt;
> > +	}
> 
> Yuk.
> 
> This really wants some luo helper
> 
> 'luo alloc array'
> 'luo restore array'
> 'luo free array'
> 
> Which would get a linearized list of pages in the vmap to hold the
> array and then allocate some structure to record the page list and
> return back the u64 of the phys_addr of the top of the structure to
> store in whatever.
> 
> Getting fdt to allocate the array inside the fds is just not going to
> work for anything of size.

I agree that we need a side-car structure for preserving large (potentially
sparse) arrays, but I think it should be a part of KHO rather than LUO.

-- 
Sincerely yours,
Mike.