[PATCH v8 36/43] arm64: mm: Add support for folding PUDs at runtime

[Ard Biesheuvel]

On Wed, 2 Oct 2024 at 11:08, Ryan Roberts <ryan.roberts at arm.com> wrote:
>
> On 01/10/2024 07:23, Ard Biesheuvel wrote:
...
> While you're at it, the Android folks will probably give you a medal
> > if you can manage 16k pages in user space, with 4k for the kernel and
> > for compat tasks.
>
> Ha - that's the ambition I started with. I have a design that I believe solved
> all the issues except one; how to present procfs information about a process to
> a different process with a larger page size. I felt there were likely going to
> be other ABI confusion edge case like that lurking.
>
> Eventually (with Rutland's help :) ) I conceded it was just a huge amount of
> work. And after talking with the Android guys, decided to park it. Perhaps
> something for the future, if there are other valid use cases. Boot time page
> size selection has value on its own, but is orthogonal to per-process page size.
>
> >
> > But seriously, I'd be happy to compare notes about this - one thing I
> > have been meaning to do is to reduce the number of configurations we
> > support, by always using 52 bits in the kernel, and allowing some kind
> > of runtime folding for user space to reduce the depth where it
> > matters.
>
> OK that's interesting. I can see some cross-over there. I think I'm on the home
> straight for an RFC. So how about I get that posted then we can have a chat?
>

Sounds good.