lkml.org 
[lkml]   [2021]   [Oct]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH v5 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array
Date
On 20.10.2021 00:24, Sean Christopherson wrote:
> On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
>> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>>
>> 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@oracle.com>
>> ---
>> 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

\
 
 \ /
  Last update: 2021-10-20 20:42    [W:0.113 / U:1.908 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site