On 20.10.2021 00:24, 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) {
(..)
+ u64 memslots_pages;
+ unsigned long nr_mmu_pages;
+
+ memslots_pages = kvm->arch.n_memslots_pages * KVM_PERMILLE_MMU_PAGES;
+ do_div(memslots_pages, 1000);
+ nr_mmu_pages = max_t(typeof(nr_mmu_pages),
+ memslots_pages, KVM_MIN_ALLOC_MMU_PAGES);
"memslots_pages" is a bit of a misnomer. Any objection to avoiding naming problems
by explicitly casting to an "unsigned long" and simply operating on nr_mmu_pages?
nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages;
nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000);
nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
E.g. the whole thing can be
if (!kvm->arch.n_requested_mmu_pages &&
(change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
unsigned long nr_mmu_pages;
if (change == KVM_MR_CREATE) {
kvm->arch.n_memslots_pages += new->npages;
} else {
WARN_ON(kvm->arch.n_memslots_pages < old->npages);
kvm->arch.n_memslots_pages -= old->npages;
}
nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages;
nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000);
The above line will set nr_mmu_pages to zero since KVM_PERMILLE_MMU_PAGES
is 20, so when integer-divided by 1000 will result in a multiplication
coefficient of zero.
nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
}
+ kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
+ }
kvm_mmu_slot_apply_flags(kvm, old, new, change);
Thanks,
Maciej
