Re: [PATCH v4 0/5] move per-vma lock into vm_area_struct

[Suren Baghdasaryan <surenb@google.com>]

On Wed, Nov 20, 2024 at 2:10 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> On Tue, Nov 19, 2024 at 04:08:21PM -0800, Suren Baghdasaryan wrote:
> > Back when per-vma locks were introduces, vm_lock was moved out of
> > vm_area_struct in [1] because of the performance regression caused by
> > false cacheline sharing. Recent investigation [2] revealed that the
> > regressions is limited to a rather old Broadwell microarchitecture and
> > even there it can be mitigated by disabling adjacent cacheline
> > prefetching, see [3].
>
> If 'struct vm_area_struct' is prone to performance issues due to
> cacheline misalignments then we should do something about the
> __randomize_layout tag for it. I imagine we can identify the fields
> which might be performance critical to be on same cacheline or different
> cacheline due to false sharing then we can divide the fields into
> different cacheline groups and fields can be __randomize_layout within
> the group. WDYT?

I think that's a good idea since shuffling these fields around does
affect performance. I can look into it once these changes get
finalized and the layout gets more stable.

>