linux-kernel - Re: [RFC PATCH 0/6] Remove device private pages from physical address space

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Message-ID: <aSm7NTtNfGcXbuwr@casper.infradead.org>
Date: Fri, 28 Nov 2025 15:09:41 +0000
From: Matthew Wilcox <willy@...radead.org>
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, jgg@...dia.com
Subject: Re: [RFC PATCH 0/6] Remove device private pages from physical
 address space

On Fri, Nov 28, 2025 at 03:41:40PM +1100, Jordan Niethe wrote:
> A consequence of placing the device private pages outside of the
> physical address space is that they no longer have a PFN. However, it is
> still necessary to be able to look up a corresponding device private
> page from a device private PTE entry, which means that we still require
> some way to index into this device private address space. This leads to
> the idea of a device private PFN. This is like a PFN but instead of

Don't call it a "device private PFN".  That's going to lead to
confusion.  Device private index?  Device memory index?

> By removing the device private pages from the physical address space,
> this RFC also opens up the possibility to moving away from tracking
> device private memory using struct pages in the future. This is
> desirable as on systems with large amounts of memory these device
> private struct pages use a signifiant amount of memory and take a
> significant amount of time to initialize.

I did tell Jerome he was making a huge mistake with his design, but
he forced it in anyway.