KVM: sort memslots by its size and use line search

Sort memslots base on its size and use line search to find it, so that the
larger memslots have better fit

The idea is from Avi
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

include/linux/kvm_host.h

@@ -231,8 +231,12 @@ struct kvm_irq_routing_table {};
 #define KVM_MEM_SLOTS_NUM (KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS)
 #endif
 
+/*
+ * Note:
+ * memslots are not sorted by id anymore, please use id_to_memslot()
+ * to get the memslot by its id.
+ */
 struct kvm_memslots {
-	int nmemslots;
 	u64 generation;
 	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
 };
@@ -310,7 +314,8 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
 
 #define kvm_for_each_memslot(memslot, slots)	\
 	for (memslot = &slots->memslots[0];	\
-	      memslot < slots->memslots + (slots)->nmemslots; memslot++)
+	      memslot < slots->memslots + KVM_MEM_SLOTS_NUM && memslot->npages;\
+		memslot++)
 
 int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id);
 void kvm_vcpu_uninit(struct kvm_vcpu *vcpu);
@@ -336,7 +341,14 @@ static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
 static inline struct kvm_memory_slot *
 id_to_memslot(struct kvm_memslots *slots, int id)
 {
-	return &slots->memslots[id];
+	int i;
+
+	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
+		if (slots->memslots[i].id == id)
+			return &slots->memslots[i];
+
+	WARN_ON(1);
+	return NULL;
 }
 
 #define HPA_MSB ((sizeof(hpa_t) * 8) - 1)

virt/kvm/kvm_main.c

@@ -440,6 +440,15 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
 
 #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
 
+static void kvm_init_memslots_id(struct kvm *kvm)
+{
+	int i;
+	struct kvm_memslots *slots = kvm->memslots;
+
+	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
+		slots->memslots[i].id = i;
+}
+
 static struct kvm *kvm_create_vm(void)
 {
 	int r, i;
@@ -465,6 +474,7 @@ static struct kvm *kvm_create_vm(void)
 	kvm->memslots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
 	if (!kvm->memslots)
 		goto out_err_nosrcu;
+	kvm_init_memslots_id(kvm);
 	if (init_srcu_struct(&kvm->srcu))
 		goto out_err_nosrcu;
 	for (i = 0; i < KVM_NR_BUSES; i++) {
@@ -630,15 +640,54 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
 }
 #endif /* !CONFIG_S390 */
 
+static struct kvm_memory_slot *
+search_memslots(struct kvm_memslots *slots, gfn_t gfn)
+{
+	struct kvm_memory_slot *memslot;
+
+	kvm_for_each_memslot(memslot, slots)
+		if (gfn >= memslot->base_gfn &&
+		      gfn < memslot->base_gfn + memslot->npages)
+			return memslot;
+
+	return NULL;
+}
+
+static int cmp_memslot(const void *slot1, const void *slot2)
+{
+	struct kvm_memory_slot *s1, *s2;
+
+	s1 = (struct kvm_memory_slot *)slot1;
+	s2 = (struct kvm_memory_slot *)slot2;
+
+	if (s1->npages < s2->npages)
+		return 1;
+	if (s1->npages > s2->npages)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * Sort the memslots base on its size, so the larger slots
+ * will get better fit.
+ */
+static void sort_memslots(struct kvm_memslots *slots)
+{
+	sort(slots->memslots, KVM_MEM_SLOTS_NUM,
+	      sizeof(struct kvm_memory_slot), cmp_memslot, NULL);
+}
+
 void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
 {
 	if (new) {
 		int id = new->id;
 		struct kvm_memory_slot *old = id_to_memslot(slots, id);
+		unsigned long npages = old->npages;
 
 		*old = *new;
-		if (id >= slots->nmemslots)
-			slots->nmemslots = id + 1;
+		if (new->npages != npages)
+			sort_memslots(slots);
 	}
 
 	slots->generation++;
@@ -980,14 +1029,7 @@ EXPORT_SYMBOL_GPL(kvm_is_error_hva);
 static struct kvm_memory_slot *__gfn_to_memslot(struct kvm_memslots *slots,
 						gfn_t gfn)
 {
-	struct kvm_memory_slot *memslot;
-
-	kvm_for_each_memslot(memslot, slots)
-		if (gfn >= memslot->base_gfn
-		    && gfn < memslot->base_gfn + memslot->npages)
-			return memslot;
-
-	return NULL;
+	return search_memslots(slots, gfn);
 }
 
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
@@ -998,20 +1040,13 @@ EXPORT_SYMBOL_GPL(gfn_to_memslot);
 
 int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 {
-	int i;
-	struct kvm_memslots *slots = kvm_memslots(kvm);
-
-	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
-		struct kvm_memory_slot *memslot = &slots->memslots[i];
+	struct kvm_memory_slot *memslot = gfn_to_memslot(kvm, gfn);
 
-		if (memslot->flags & KVM_MEMSLOT_INVALID)
-			continue;
+	if (!memslot || memslot->id >= KVM_MEMORY_SLOTS ||
+	      memslot->flags & KVM_MEMSLOT_INVALID)
+		return 0;
 
-		if (gfn >= memslot->base_gfn
-		    && gfn < memslot->base_gfn + memslot->npages)
-			return 1;
-	}
-	return 0;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);