linux-kernel - Re: [RFC PATCH 6/6] mm: Remove device private pages from the physical address space

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Message-ID: <20251128175108.GG812105@ziepe.ca>
Date: Fri, 28 Nov 2025 13:51:08 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Jordan Niethe <jniethe@...dia.com>
Cc: linux-mm@...ck.org, balbirs@...dia.com, matthew.brost@...el.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, david@...hat.com, ziy@...dia.com,
	apopple@...dia.com, lorenzo.stoakes@...cle.com, lyude@...hat.com,
	dakr@...nel.org, airlied@...il.com, simona@...ll.ch,
	rcampbell@...dia.com, mpenttil@...hat.com, willy@...radead.org
Subject: Re: [RFC PATCH 6/6] mm: Remove device private pages from the
 physical address space

On Fri, Nov 28, 2025 at 03:41:46PM +1100, Jordan Niethe wrote:
> Introduce helpers:
> 
>   - device_private_page_to_offset()
>   - device_private_folio_to_offset()
> 
> to take a given device private page / folio and return its offset within
> the device private address space (this is essentially a PFN within the
> device private address space).

It would be nice if we rarely/never needed to see number space outside
the pte itself or the internal helpers..

Like, I don't think there should be stuff like this:

>  					entry = make_writable_migration_device_private_entry(
> -								page_to_pfn(page));
> +								device_private_page_to_offset(page));

make_writable_migration_device_private_entry() should accept the
struct page as the handle?

If it really is needed I think it should have its own dedicated type
and not be intermixed with normal pfns..

Jason