Commit ebdb292d authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Batch zap MMU pages when shrinking the slab 



Use the recently introduced kvm_mmu_zap_oldest_mmu_pages() to batch zap
MMU pages when shrinking a slab.  This fixes a long standing issue where
KVM's shrinker implementation is completely ineffective due to zapping
only a single page.  E.g. without batch zapping, forcing a scan via
drop_caches basically has no impact on a VM with ~2k shadow pages.  With
batch zapping, the number of shadow pages can be reduced to a few
hundred pages in one or two runs of drop_caches.

Note, if the default batch size (currently 128) is problematic, e.g.
zapping 128 pages holds mmu_lock for too long, KVM can bound the batch
size by setting @batch in mmu_shrinker.

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200623193542.7554-4-sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 6b82ef2c

arch/x86/kvm/mmu/mmu.c

+1 −16
Original line number Diff line number Diff line
@@ -2816,19 +2816,6 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, 
	}

}



static bool prepare_zap_oldest_mmu_page(struct kvm *kvm,

					struct list_head *invalid_list)

{

	struct kvm_mmu_page *sp;



	if (list_empty(&kvm->arch.active_mmu_pages))

		return false;



	sp = list_last_entry(&kvm->arch.active_mmu_pages,

			     struct kvm_mmu_page, link);

	return kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);

}



static unsigned long kvm_mmu_zap_oldest_mmu_pages(struct kvm *kvm,

						  unsigned long nr_to_zap)

{
@@ -6116,9 +6103,7 @@ mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) 
			goto unlock;

		}



		if (prepare_zap_oldest_mmu_page(kvm, &invalid_list))

			freed++;

		kvm_mmu_commit_zap_page(kvm, &invalid_list);

		freed = kvm_mmu_zap_oldest_mmu_pages(kvm, sc->nr_to_scan);



unlock:

		spin_unlock(&kvm->mmu_lock);