Re: [PATCH 01/14] mm: decouple protnone helpers from CONFIG_NUMA_BALANCING

[SeongJae Park <sj@kernel.org>]

On Mon, 27 Apr 2026 12:45:49 +0100 "Kiryl Shutsemau (Meta)" <kas@kernel.org> wrote:

> pte_protnone() and pmd_protnone() detect present-but-inaccessible page
> table entries. This capability is useful beyond NUMA balancing — for
> example, userfaultfd working set tracking uses protnone PTEs to track
> page access without unmapping pages.

I agree.  It can be useful for general access monitoring.  I'm also slowly but
continuously working [1] to use that for DAMON.

> 
> Introduce CONFIG_ARCH_HAS_PTE_PROTNONE to decouple the protnone PTE
> infrastructure from CONFIG_NUMA_BALANCING. The six architectures that
> support protnone PTEs (x86_64, arm64, powerpc, s390, riscv, loongarch)
> now select this option, and CONFIG_NUMA_BALANCING depends on it.
> 
> No functional change — the same set of architectures continues to have
> working protnone support, but the infrastructure is now available
> independently of NUMA balancing.

I think this is a good change for making the infrastructure available for uffd.
I believe this can also be useful for making it further available for general
access monitoring purposes.  I hope this to be landed on the mainline sooner
than later.  Thank you for doing this, Kiryl!

> 
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> Assisted-by: Claude:claude-opus-4-6

Acked-by: SeongJae Park <sj@kernel.org>

[1] https://lore.kernel.org/linux-mm/20260218054320.4570-1-sj@kernel.org/

Thanks,
SJ

[...]