Re: [PATCH v6 1/5] mm: Make per-VMA locks available universally

On 8/13/26 21:34, Suren Baghdasaryan wrote:

From: Dave Hansen <dave.hansen@linux.intel.com>

The per-VMA locks have been around for several years. They've had some
bugs worked out of them and have seen quite wide use. However, they
are still only available when architectures explicitly enable them.
Remove the conditional compilation around the per-VMA locks, making
them available on all architectures and configs.

The approach up to now seemed to be to add ARCH_SUPPORTS_PER_VMA_LOCK
when the architecture started using per-VMA locks in the fault
handler. But, contrary to the naming, the Kconfig option does not
really indicate whether the architecture supports per-VMA locks or
not. It is more of a marker for whether the architecture is likely to
benefit from per-VMA locks.

To me, the most important thing side-effect of universal availability
is letting per-VMA locks be used in SMP=n configs. This lets us use
per-VMA locking in all x86 code without fallbacks.

Overall, this just generally makes the kernel simpler. Just look at
the diffstat. It also opens the door to users that want to use the
per-VMA locks in common code. Doing *that* brings additional
simplifications.

The downside of this is adding some fields to vm_area_struct and
mm_struct. There are likely ways to optimize this, especially for
things like SMP=n configs. For now, do the simplest thing: use the
same implementation everywhere.

== Considerations for NOMMU config ==

Maybe the NOMMU "support" could have been had in a separate prep patch (where a
lot of the description below could have been moved), making the patch itself
just mostly a removal of code.


Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David