Re: [PATCH v3 0/7] mm/kvm: Improve parallelism for access bit harvesting

James Houghton
2024-04-19T20:57:40Z

On Fri, Apr 12, 2024 at 11:41 AM David Matlack <dmatlack@google.com> wrote:
>
> On 2024-04-01 11:29 PM, James Houghton wrote:
> > This patchset adds a fast path in KVM to test and clear access bits on
> > sptes without taking the mmu_lock. It also adds support for using a
> > bitmap to (1) test the access bits for many sptes in a single call to
> > mmu_notifier_test_young, and to (2) clear the access bits for many ptes
> > in a single call to mmu_notifier_clear_young.
>
> How much improvement would we get if we _just_ made test/clear_young
> lockless on x86 and hold the read-lock on arm64? And then how much
> benefit does the bitmap look-around add on top of that?

I don't have these results right now. For the next version I will (1)
separate the series into the locking change and the bitmap change, and
I will (2) have performance data for each change separately. It is
conceivable that the bitmap change should just be considered as a
completely separate patchset.