Re: [PATCH v4 1/5] mm: Make per-VMA locks available universally

[Dave Hansen]

On 8/10/26 03:17, Lorenzo Stoakes (ARM) wrote:
> On Thu, Aug 06, 2026 at 01:05:44PM -0700, Suren Baghdasaryan wrote:
...
>> 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.
> 
> I think for most cases SMP=n arches are not going to be scaling too crazily
> on threads/processes anyway.
> 
> If real world usecases exist that the struct bloat causes problems for then
> optimisations for those can be looked into.

Yup, totally agree. It's not worth adding complexity and bugs when the
gains would be small.

> But I wonder if cache line alignment would in any case alter the impact of
> this anyway?

Yes, the CONFIG_PER_VMA_LOCK structures are spread across a couple of
spots in vm_area_struct. At least one of them is 4 bytes and another is
____cacheline_aligned_in_smp. I'd eat my hat if there aren't at least a
couple of bytes that could be trimmed.