On Wed, 26 Apr 2023 17:23:18 +0000, Ricardo Koller wrote:
> Eager Page Splitting improves the performance of dirty-logging (used
> in live migrations) when guest memory is backed by huge-pages. It's
> an optimization used in Google Cloud since 2016 on x86, and for the
> last couple of months on ARM.
>
> Background and motivation
> =========================
> Dirty logging is typically used for live-migration iterative copying.
> KVM implements dirty-logging at the PAGE_SIZE granularity (will refer
> to 4K pages from now on). It does it by faulting on write-protected
> 4K pages. Therefore, enabling dirty-logging on a huge-page requires
> breaking it into 4K pages in the first place. KVM does this breaking
> on fault, and because it's in the critical path it only maps the 4K
> page that faulted; every other 4K page is left unmapped. This is not
> great for performance on ARM for a couple of reasons:
>
> [...]
Picking these patches up early, as I'd like to get some mileage on the
patches well in advance of 6.5.
Applied to kvmarm/next, thanks!
[01/12] KVM: arm64: Rename free_removed to free_unlinked
https://git.kernel.org/kvmarm/kvmarm/c/c14d08c5adb2
[02/12] KVM: arm64: Add KVM_PGTABLE_WALK flags for skipping CMOs and BBM TLBIs
https://git.kernel.org/kvmarm/kvmarm/c/02f10845f435
[03/12] KVM: arm64: Add helper for creating unlinked stage2 subtrees
https://git.kernel.org/kvmarm/kvmarm/c/e7c05540c694
[04/12] KVM: arm64: Export kvm_are_all_memslots_empty()
https://git.kernel.org/kvmarm/kvmarm/c/26f457142d7e
[05/12] KVM: arm64: Add KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE
https://git.kernel.org/kvmarm/kvmarm/c/2f440b72e852
[06/12] KVM: arm64: Add kvm_pgtable_stage2_split()
https://git.kernel.org/kvmarm/kvmarm/c/8f5a3eb7513f
[07/12] KVM: arm64: Refactor kvm_arch_commit_memory_region()
https://git.kernel.org/kvmarm/kvmarm/c/6bd92b9d8b02
[08/12] KVM: arm64: Add kvm_uninit_stage2_mmu()
https://git.kernel.org/kvmarm/kvmarm/c/ce2b60223800
[09/12] KVM: arm64: Split huge pages when dirty logging is enabled
https://git.kernel.org/kvmarm/kvmarm/c/e7bf7a490c68
[10/12] KVM: arm64: Open-code kvm_mmu_write_protect_pt_masked()
https://git.kernel.org/kvmarm/kvmarm/c/3005f6f29447
[11/12] KVM: arm64: Split huge pages during KVM_CLEAR_DIRTY_LOG
https://git.kernel.org/kvmarm/kvmarm/c/6acf51666d03
[12/12] KVM: arm64: Use local TLBI on permission relaxation
https://git.kernel.org/kvmarm/kvmarm/c/a12ab1378a88
--
Best,
Oliver
