On 20.10.2021 00:31, Sean Christopherson wrote:
On Tue, Oct 19, 2021, Sean Christopherson wrote:
On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
From: "Maciej S. Szmigiero" <maciej.szmigiero@xxxxxxxxxx>
There is no point in recalculating from scratch the total number of pages
in all memslots each time a memslot is created or deleted.
Just cache the value and update it accordingly on each such operation so
the code doesn't need to traverse the whole memslot array each time.
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@xxxxxxxxxx>
---
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 28ef14155726..65fdf27b9423 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11609,9 +11609,23 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
const struct kvm_memory_slot *new,
enum kvm_mr_change change)
{
- if (!kvm->arch.n_requested_mmu_pages)
- kvm_mmu_change_mmu_pages(kvm,
- kvm_mmu_calculate_default_mmu_pages(kvm));
+ if (change == KVM_MR_CREATE)
+ kvm->arch.n_memslots_pages += new->npages;
+ else if (change == KVM_MR_DELETE) {
+ WARN_ON(kvm->arch.n_memslots_pages < old->npages);
+ kvm->arch.n_memslots_pages -= old->npages;
+ }
+
+ if (!kvm->arch.n_requested_mmu_pages) {
Hmm, once n_requested_mmu_pages is set it can't be unset. That means this can be
further optimized to skip avoid taking mmu_lock on flags-only changes (and
memslot movement). E.g.
if (!kvm->arch.n_requested_mmu_pages &&
(change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
}
It's a little risky, but kvm_vm_ioctl_set_nr_mmu_pages() would need to be modified
to allow clearing n_requested_mmu_pages and it already takes slots_lock, so IMO
it's ok to force kvm_vm_ioctl_set_nr_mmu_pages() to recalculate pages if it wants
to allow reverting back to the default.
Doh, and then I read patch 2...
I would swap the order of patch 2 and patch 1, that way the optimization patch is
super simple, and you don't end up reworking a bunch of code that was added in the
immediately preceding patch. E.g. as a first patch
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 28ef14155726..f3b1aed08566 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11609,7 +11609,8 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
const struct kvm_memory_slot *new,
enum kvm_mr_change change)
{
- if (!kvm->arch.n_requested_mmu_pages)
+ if (!kvm->arch.n_requested_mmu_pages &&
+ (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
kvm_mmu_change_mmu_pages(kvm,
kvm_mmu_calculate_default_mmu_pages(kvm));
Will do.
Thanks,
Maciej
