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

On Wed,  7 Jan 2026 20:18:12 +1100 Jordan Niethe [off-list ref] 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.