Re: [PATCH v2 00/11] Remove device private pages from physical address space

Andrew Morton
2026-01-07T20:06:17Z

On Wed, 7 Jan 2026 20:18:12 +1100 Jordan Niethe <jniethe@nvidia.com> wrote:

> Today, when creating these device private struct pages, the first step
> is to use request_free_mem_region() to get a range of physical address
> space large enough to represent the devices memory. This allocated
> physical address range is then remapped as device private memory using
> memremap_pages.

Welcome to Linux MM. That's a heck of an opening salvo ;)

> Needing allocation of physical address space has some problems:
>
> 1) There may be insufficient physical address space to represent the
> device memory. KASLR reducing the physical address space and VM
> configurations with limited physical address space increase the
> likelihood of hitting this especially as device memory increases. This
> has been observed to prevent device private from being initialized.
>
> 2) Attempting to add the device private pages to the linear map at
> addresses beyond the actual physical memory causes issues on
> architectures like aarch64 - meaning the feature does not work there [0].

Can you better help us understand the seriousness of these problems?
How much are our users really hurting from this?

> Seeking opinions on using the mpfns like this or if a new type would be
> preferred.

Whose opinions? IOW, can you suggest who you'd like to see review this
work?

>
> * NOTE: I will need help in testing the driver changes *
>

Again, please name names ;) I'm not afraid to prod.

I'm reluctant to add this to mm.git's development/testing branches at
this time. Your advice on when you think we're ready for that step
would be valuable, thanks.