KVM: MMU: Introduce a helper function for FIFO zapping

Make the code for zapping the oldest mmu page, placed at the tail of the
active list, a separate function.
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -2110,6 +2110,21 @@ 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_entry(kvm->arch.active_mmu_pages.prev,
+			struct kvm_mmu_page, link);
+	kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
+
+	return true;
+}
+
 /*
  * Changing the number of mmu pages allocated to the vm
  * Note: if goal_nr_mmu_pages is too small, you will get dead lock
@@ -2117,23 +2132,15 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int goal_nr_mmu_pages)
 {
 	LIST_HEAD(invalid_list);
-	/*
-	 * If we set the number of mmu pages to be smaller be than the
-	 * number of actived pages , we must to free some mmu pages before we
-	 * change the value
-	 */
 
 	spin_lock(&kvm->mmu_lock);
 
 	if (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages) {
-		while (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages &&
-			!list_empty(&kvm->arch.active_mmu_pages)) {
-			struct kvm_mmu_page *page;
+		/* Need to free some mmu pages to achieve the goal. */
+		while (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages)
+			if (!prepare_zap_oldest_mmu_page(kvm, &invalid_list))
+				break;
 
-			page = container_of(kvm->arch.active_mmu_pages.prev,
-					    struct kvm_mmu_page, link);
-			kvm_mmu_prepare_zap_page(kvm, page, &invalid_list);
-		}
 		kvm_mmu_commit_zap_page(kvm, &invalid_list);
 		goal_nr_mmu_pages = kvm->arch.n_used_mmu_pages;
 	}
@@ -4007,13 +4014,10 @@ void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
 {
 	LIST_HEAD(invalid_list);
 
-	while (kvm_mmu_available_pages(vcpu->kvm) < KVM_REFILL_PAGES &&
-	       !list_empty(&vcpu->kvm->arch.active_mmu_pages)) {
-		struct kvm_mmu_page *sp;
+	while (kvm_mmu_available_pages(vcpu->kvm) < KVM_REFILL_PAGES) {
+		if (!prepare_zap_oldest_mmu_page(vcpu->kvm, &invalid_list))
+			break;
 
-		sp = container_of(vcpu->kvm->arch.active_mmu_pages.prev,
-				  struct kvm_mmu_page, link);
-		kvm_mmu_prepare_zap_page(vcpu->kvm, sp, &invalid_list);
 		++vcpu->kvm->stat.mmu_recycled;
 	}
 	kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
@@ -4182,19 +4186,6 @@ void kvm_mmu_zap_all(struct kvm *kvm)
 	spin_unlock(&kvm->mmu_lock);
 }
 
-static void kvm_mmu_remove_some_alloc_mmu_pages(struct kvm *kvm,
-						struct list_head *invalid_list)
-{
-	struct kvm_mmu_page *page;
-
-	if (list_empty(&kvm->arch.active_mmu_pages))
-		return;
-
-	page = container_of(kvm->arch.active_mmu_pages.prev,
-			    struct kvm_mmu_page, link);
-	kvm_mmu_prepare_zap_page(kvm, page, invalid_list);
-}
-
 static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
 {
 	struct kvm *kvm;
@@ -4229,7 +4220,7 @@ static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
 		idx = srcu_read_lock(&kvm->srcu);
 		spin_lock(&kvm->mmu_lock);
 
-		kvm_mmu_remove_some_alloc_mmu_pages(kvm, &invalid_list);
+		prepare_zap_oldest_mmu_page(kvm, &invalid_list);
 		kvm_mmu_commit_zap_page(kvm, &invalid_list);
 
 		spin_unlock(&kvm->mmu_lock);