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

[Andrew Morton]

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