Messages in this thread | | | Subject | Re: [PATCH v2 0/7] Lazily allocate memslot rmaps | From | Paolo Bonzini <> | Date | Mon, 3 May 2021 15:44:56 +0200 |
| |
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!
Paolo
> Changelog: > v2: > Incorporated feedback from Paolo and Sean > Replaced the memslot_assignment_lock with slots_arch_lock, which > has a larger critical section. > > Ben Gardon (7): > KVM: x86/mmu: Track if shadow MMU active > KVM: x86/mmu: Skip rmap operations if shadow MMU inactive > KVM: x86/mmu: Deduplicate rmap freeing > KVM: x86/mmu: Factor out allocating memslot rmap > KVM: mmu: Refactor memslot copy > KVM: mmu: Add slots_arch_lock for memslot arch fields > KVM: x86/mmu: Lazily allocate memslot rmaps > > arch/x86/include/asm/kvm_host.h | 13 +++ > arch/x86/kvm/mmu/mmu.c | 153 +++++++++++++++++++++----------- > arch/x86/kvm/mmu/mmu_internal.h | 2 + > arch/x86/kvm/mmu/tdp_mmu.c | 6 +- > arch/x86/kvm/mmu/tdp_mmu.h | 4 +- > arch/x86/kvm/x86.c | 110 +++++++++++++++++++---- > include/linux/kvm_host.h | 9 ++ > virt/kvm/kvm_main.c | 54 ++++++++--- > 8 files changed, 264 insertions(+), 87 deletions(-) >
| |