Re: [PATCH v2 0/7] Lazily allocate memslot rmaps

[Paolo Bonzini]

On 03/05/21 19:31, Ben Gardon wrote:
> On Mon, May 3, 2021 at 6:45 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> > On 29/04/21 23:18, Ben Gardon wrote:
> > > This series enables KVM to save memory when using the TDP MMU by waiting
> > > to allocate memslot rmaps until they are needed. To do this, KVM tracks
> > > whether or not a shadow root has been allocated. In order to get away
> > > with not allocating the rmaps, KVM must also be sure to skip operations
> > > which iterate over the rmaps. If the TDP MMU is in use and we have not
> > > allocated a shadow root, these operations would essentially be op-ops
> > > anyway. Skipping the rmap operations has a secondary benefit of avoiding
> > > acquiring the MMU lock in write mode in many cases, substantially
> > > reducing MMU lock contention.
> > >
> > > This series was tested on an Intel Skylake machine. With the TDP MMU off
> > > and on, this introduced no new failures on kvm-unit-tests or KVM selftests.
> >
> > Thanks, I only reported some technicalities in the ordering of loads
> > (which matter since the loads happen with SRCU protection only).  Apart
> > from this, this looks fine!
>
> Awesome to hear, thank you for the reviews. Should I send a v3
> addressing those comments, or did you already make those changes when
> applying to your tree?

No, I didn't (I wanted some oversight, and this is 5.14 stuff anyway).

Paolo