diff --git a/lib/isc/astack.c b/lib/isc/astack.c
index d67df51181..0d494fa94b 100644
--- a/lib/isc/astack.c
+++ b/lib/isc/astack.c
@@ -19,65 +19,123 @@
 #include <isc/types.h>
 #include <isc/util.h>
 
-struct isc_astack {
-	isc_mem_t *mctx;
+typedef struct nodes {
 	size_t size;
 	size_t pos;
+	void **nodes;
+} nodes_t;
+
+struct isc_astack {
+	isc_mem_t *mctx;
 	isc_mutex_t lock;
-	uintptr_t nodes[];
+	size_t min_size;
+	size_t max_size;
+	nodes_t cur;
+	nodes_t old;
 };
 
-isc_astack_t *
-isc_astack_new(isc_mem_t *mctx, size_t size) {
-	isc_astack_t *stack = isc_mem_get(
-		mctx, sizeof(isc_astack_t) + size * sizeof(uintptr_t));
+static void
+nodes_new(isc_mem_t *mctx, nodes_t *cur, size_t size) {
+	*cur = (nodes_t){ .size = size };
 
-	*stack = (isc_astack_t){
-		.size = size,
-	};
+	if (size > 0) {
+		cur->nodes = isc_mem_get(mctx, cur->size * sizeof(void *));
+		memset(cur->nodes, 0, cur->size * sizeof(void *));
+	}
+}
+
+static void
+nodes_free(isc_mem_t *mctx, nodes_t *cur) {
+	REQUIRE(cur->pos == 0);
+
+	if (cur->size > 0) {
+		REQUIRE(cur->nodes != NULL);
+		isc_mem_put(mctx, cur->nodes, cur->size * sizeof(void *));
+	}
+
+	*cur = (nodes_t){ .size = 0 };
+}
+
+#define IS_POWEROF2(bits) (bits && !(bits & (bits - 1)))
+
+isc_astack_t *
+isc_astack_new(isc_mem_t *mctx, size_t min_size, size_t max_size) {
+	isc_astack_t *stack = isc_mem_get(mctx, sizeof(isc_astack_t));
+
+	REQUIRE(IS_POWEROF2(min_size));
+	REQUIRE(IS_POWEROF2(max_size));
+
+	*stack = (isc_astack_t){ .min_size = min_size, .max_size = max_size };
 	isc_mem_attach(mctx, &stack->mctx);
-	memset(stack->nodes, 0, size * sizeof(uintptr_t));
 	isc_mutex_init(&stack->lock);
+
+	nodes_new(mctx, &stack->cur, stack->min_size);
+	nodes_new(mctx, &stack->old, 0);
+
 	return (stack);
 }
 
 bool
 isc_astack_trypush(isc_astack_t *stack, void *obj) {
-	if (!isc_mutex_trylock(&stack->lock)) {
-		if (stack->pos >= stack->size) {
+	if (isc_mutex_trylock(&stack->lock) != ISC_R_SUCCESS) {
+		return (false);
+	}
+
+	if (stack->cur.pos >= stack->cur.size) {
+		if (stack->old.size > 0) {
 			UNLOCK(&stack->lock);
 			return (false);
 		}
-		stack->nodes[stack->pos++] = (uintptr_t)obj;
-		UNLOCK(&stack->lock);
-		return (true);
-	} else {
-		return (false);
+
+		if (stack->cur.size * 2 > stack->max_size) {
+			UNLOCK(&stack->lock);
+			return (false);
+		}
+
+		stack->old = stack->cur;
+		nodes_new(stack->mctx, &stack->cur, stack->old.size * 2);
 	}
+
+	stack->cur.nodes[stack->cur.pos++] = obj;
+	UNLOCK(&stack->lock);
+	return (true);
 }
 
 void *
 isc_astack_pop(isc_astack_t *stack) {
-	LOCK(&stack->lock);
-	uintptr_t rv;
-	if (stack->pos == 0) {
-		rv = 0;
+	void *rv;
+
+	if (isc_mutex_trylock(&stack->lock) != ISC_R_SUCCESS) {
+		return (false);
+	}
+
+	if (stack->old.size > 0) {
+		REQUIRE(stack->old.pos > 0);
+
+		rv = stack->old.nodes[--stack->old.pos];
+
+		if (stack->old.pos == 0) {
+			nodes_free(stack->mctx, &stack->old);
+		}
+	} else if (stack->cur.pos > 0) {
+		rv = stack->cur.nodes[--stack->cur.pos];
 	} else {
-		rv = stack->nodes[--stack->pos];
+		rv = NULL;
 	}
 	UNLOCK(&stack->lock);
-	return ((void *)rv);
+	return (rv);
 }
 
 void
 isc_astack_destroy(isc_astack_t *stack) {
 	LOCK(&stack->lock);
-	REQUIRE(stack->pos == 0);
+	REQUIRE(stack->cur.pos == 0);
+	REQUIRE(stack->old.size == 0);
 	UNLOCK(&stack->lock);
 
+	nodes_free(stack->mctx, &stack->cur);
+
 	isc_mutex_destroy(&stack->lock);
 
-	isc_mem_putanddetach(&stack->mctx, stack,
-			     sizeof(struct isc_astack) +
-				     stack->size * sizeof(uintptr_t));
+	isc_mem_putanddetach(&stack->mctx, stack, sizeof(struct isc_astack));
 }
diff --git a/lib/isc/include/isc/astack.h b/lib/isc/include/isc/astack.h
index c85fee64d1..0f55fc45f3 100644
--- a/lib/isc/include/isc/astack.h
+++ b/lib/isc/include/isc/astack.h
@@ -17,9 +17,10 @@
 #include <isc/types.h>
 
 isc_astack_t *
-isc_astack_new(isc_mem_t *mctx, size_t size);
+isc_astack_new(isc_mem_t *mctx, size_t min_size, size_t max_size);
 /*%<
- * Allocate and initialize a new array stack of size 'size'.
+ * Allocate and initialize a new bounded array stack.  Initially, min_size
+ * entries will be allocated, but would grow up to max_size entries.
  */
 
 void
diff --git a/lib/isc/netmgr/netmgr.c b/lib/isc/netmgr/netmgr.c
index e81ad4673e..5498c22e54 100644
--- a/lib/isc/netmgr/netmgr.c
+++ b/lib/isc/netmgr/netmgr.c
@@ -48,8 +48,11 @@
  * How many isc_nmhandles and isc_nm_uvreqs will we be
  * caching for reuse in a socket.
  */
-#define ISC_NM_HANDLES_STACK_SIZE 600
-#define ISC_NM_REQS_STACK_SIZE	  600
+#define ISC_NM_HANDLES_MIN_STACK_SIZE 32
+#define ISC_NM_HANDLES_MAX_STACK_SIZE 1024
+
+#define ISC_NM_REQS_MIN_STACK_SIZE 32
+#define ISC_NM_REQS_MAX_STACK_SIZE 1024
 
 /*%
  * Shortcut index arrays to get access to statistics counters.
@@ -1441,14 +1444,20 @@ isc___nmsocket_init(isc_nmsocket_t *sock, isc_nm_t *mgr, isc_nmsocket_type type,
 
 	family = iface->type.sa.sa_family;
 
-	*sock = (isc_nmsocket_t){ .type = type,
-				  .iface = *iface,
-				  .fd = -1,
-				  .ah_size = 32,
-				  .inactivehandles = isc_astack_new(
-					  mgr->mctx, ISC_NM_HANDLES_STACK_SIZE),
-				  .inactivereqs = isc_astack_new(
-					  mgr->mctx, ISC_NM_REQS_STACK_SIZE) };
+	*sock = (isc_nmsocket_t){
+		.type = type,
+		.iface = *iface,
+		.fd = -1,
+		.ah_size = 32,
+	};
+
+	sock->inactivehandles = isc_astack_new(mgr->mctx,
+					       ISC_NM_HANDLES_MIN_STACK_SIZE,
+					       ISC_NM_HANDLES_MAX_STACK_SIZE);
+
+	sock->inactivereqs = isc_astack_new(mgr->mctx,
+					    ISC_NM_REQS_MIN_STACK_SIZE,
+					    ISC_NM_REQS_MAX_STACK_SIZE);
 
 #if NETMGR_TRACE
 	sock->backtrace_size = backtrace(sock->backtrace, TRACE_SIZE);