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

Jordan Niethe
2025-12-02T01:31:44Z

Hi,

On 29/11/25 02:09, Matthew Wilcox wrote:
> 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?

Sure, I think 'device memory index' is fine. What I was trying to
express with 'device private PFN' here is that each index into device
memory still represents a PAGE_SIZE region, but I agree it leads to
further confusion.

Thanks,
Jordan.

>
>> 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.