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

[Sean Christopherson <seanjc@google.com>]

On Tue, May 04, 2021, Ben Gardon wrote:
> On Tue, May 4, 2021 at 12:21 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
> >
> > On 03/05/21 19:31, Ben Gardon wrote:
> > > On Mon, May 3, 2021 at 6:45 AM Paolo Bonzini <pbonzini@redhat.com> 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).
> 
> Ah, okay I'll send out a v3 soon, discussion on the other patches settles.

I'll look through v2 this afternoon, now that I've mostly dug myself out of
RDPID hell.