forked from Minki/linux
KVM: MMU: zap pages in batch
Zap at lease 10 pages before releasing mmu-lock to reduce the overload caused by requiring lock After the patch, kvm_zap_obsolete_pages can forward progress anyway, so update the comments [ It improves the case 0.6% ~ 1% that do kernel building meanwhile read PCI ROM. ] Note: i am not sure that "10" is the best speculative value, i just guessed that '10' can make vcpu do not spend long time on kvm_zap_obsolete_pages and do not cause mmu-lock too hungry. Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Gleb Natapov <gleb@redhat.com>
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@ -4197,14 +4197,18 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
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spin_unlock(&kvm->mmu_lock);
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}
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#define BATCH_ZAP_PAGES 10
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static void kvm_zap_obsolete_pages(struct kvm *kvm)
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{
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struct kvm_mmu_page *sp, *node;
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LIST_HEAD(invalid_list);
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int batch = 0;
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restart:
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list_for_each_entry_safe_reverse(sp, node,
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&kvm->arch.active_mmu_pages, link) {
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int ret;
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/*
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* No obsolete page exists before new created page since
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* active_mmu_pages is the FIFO list.
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@ -4213,28 +4217,6 @@ restart:
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break;
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/*
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* Do not repeatedly zap a root page to avoid unnecessary
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* KVM_REQ_MMU_RELOAD, otherwise we may not be able to
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* progress:
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* vcpu 0 vcpu 1
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* call vcpu_enter_guest():
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* 1): handle KVM_REQ_MMU_RELOAD
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* and require mmu-lock to
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* load mmu
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* repeat:
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* 1): zap root page and
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* send KVM_REQ_MMU_RELOAD
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*
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* 2): if (cond_resched_lock(mmu-lock))
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*
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* 2): hold mmu-lock and load mmu
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*
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* 3): see KVM_REQ_MMU_RELOAD bit
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* on vcpu->requests is set
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* then return 1 to call
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* vcpu_enter_guest() again.
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* goto repeat;
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*
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* Since we are reversely walking the list and the invalid
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* list will be moved to the head, skip the invalid page
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* can help us to avoid the infinity list walking.
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@ -4242,13 +4224,18 @@ restart:
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if (sp->role.invalid)
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continue;
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if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
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if (batch >= BATCH_ZAP_PAGES &&
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(need_resched() || spin_needbreak(&kvm->mmu_lock))) {
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batch = 0;
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kvm_mmu_commit_zap_page(kvm, &invalid_list);
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cond_resched_lock(&kvm->mmu_lock);
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goto restart;
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}
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if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
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ret = kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
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batch += ret;
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if (ret)
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goto restart;
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}
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