diff --git a/crates/shadowsocks-service/src/local/loadbalancing/ping_balancer.rs b/crates/shadowsocks-service/src/local/loadbalancing/ping_balancer.rs
index c2f0c7a058ea..835caac0b561 100644
--- a/crates/shadowsocks-service/src/local/loadbalancing/ping_balancer.rs
+++ b/crates/shadowsocks-service/src/local/loadbalancing/ping_balancer.rs
@@ -71,7 +71,7 @@ impl PingBalancerBuilder {
     pub async fn build(self) -> (PingBalancer, impl Future<Output = ()>) {
         assert!(!self.servers.is_empty(), "build PingBalancer without any servers");
 
-        let balancer = PingBalancerInner {
+        let balancer_context = PingBalancerContext {
             servers: self.servers,
             best_tcp_idx: AtomicUsize::new(0),
             best_udp_idx: AtomicUsize::new(0),
@@ -79,25 +79,29 @@ impl PingBalancerBuilder {
             mode: self.mode,
         };
 
-        balancer.init_score().await;
+        balancer_context.init_score().await;
 
-        let shared = Arc::new(balancer);
-        let inner = shared.clone();
+        let shared_context = Arc::new(balancer_context);
 
-        let (checker, abortable) = future::abortable(async move { shared.checker_task().await });
+        let (checker, abortable) = {
+            let shared_context = shared_context.clone();
+            future::abortable(async move { shared_context.checker_task().await })
+        };
         let checker = async move {
             let _ = checker.await;
         };
 
         let balancer = PingBalancer {
-            inner,
-            abortable: Arc::new(abortable),
+            inner: Arc::new(PingBalancerInner {
+                context: shared_context,
+                abortable,
+            }),
         };
         (balancer, checker)
     }
 }
 
-struct PingBalancerInner {
+struct PingBalancerContext {
     servers: Vec<Arc<ServerIdent>>,
     best_tcp_idx: AtomicUsize,
     best_udp_idx: AtomicUsize,
@@ -105,7 +109,7 @@ struct PingBalancerInner {
     mode: Mode,
 }
 
-impl PingBalancerInner {
+impl PingBalancerContext {
     fn best_tcp_server(&self) -> Arc<ServerIdent> {
         self.servers[self.best_tcp_idx.load(Ordering::Relaxed)].clone()
     }
@@ -115,7 +119,7 @@ impl PingBalancerInner {
     }
 }
 
-impl PingBalancerInner {
+impl PingBalancerContext {
     async fn init_score(&self) {
         assert!(!self.servers.is_empty(), "check PingBalancer without any servers");
 
@@ -141,7 +145,10 @@ impl PingBalancerInner {
 
     /// Check each servers' score and update the best server's index
     async fn check_once(&self, print_switch: bool) {
-        let mut vfut = Vec::with_capacity(self.servers.len());
+        let mut vfut = match self.mode {
+            Mode::TcpAndUdp => Vec::with_capacity(self.servers.len() * 2),
+            Mode::TcpOnly | Mode::UdpOnly => Vec::with_capacity(self.servers.len()),
+        };
 
         for server in self.servers.iter() {
             if self.mode.enable_tcp() {
@@ -232,47 +239,52 @@ impl PingBalancerInner {
     }
 }
 
-/// Balancer with active probing
-#[derive(Clone)]
-pub struct PingBalancer {
-    inner: Arc<PingBalancerInner>,
-    abortable: Arc<AbortHandle>,
+struct PingBalancerInner {
+    context: Arc<PingBalancerContext>,
+    abortable: AbortHandle,
 }
 
-impl Drop for PingBalancer {
+impl Drop for PingBalancerInner {
     fn drop(&mut self) {
         self.abortable.abort();
+        trace!("ping balancer stopped");
     }
 }
 
+/// Balancer with active probing
+#[derive(Clone)]
+pub struct PingBalancer {
+    inner: Arc<PingBalancerInner>,
+}
+
 impl PingBalancer {
     /// Get service context
     pub fn context(&self) -> Arc<ServiceContext> {
-        self.inner.context.clone()
+        self.inner.context.context.clone()
     }
 
     /// Get reference of the service context
     pub fn context_ref(&self) -> &ServiceContext {
-        self.inner.context.as_ref()
+        self.inner.context.context.as_ref()
     }
 
     /// Pick the best TCP server
     pub fn best_tcp_server(&self) -> Arc<ServerIdent> {
-        self.inner.best_tcp_server()
+        self.inner.context.best_tcp_server()
     }
 
     /// Pick the best UDP server
     pub fn best_udp_server(&self) -> Arc<ServerIdent> {
-        self.inner.best_udp_server()
+        self.inner.context.best_udp_server()
     }
 }
 
 impl Debug for PingBalancer {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("PingBalancer")
-            .field("servers", &self.inner.servers)
-            .field("best_tcp_idx", &self.inner.best_tcp_idx.load(Ordering::Relaxed))
-            .field("best_udp_idx", &self.inner.best_udp_idx.load(Ordering::Relaxed))
+            .field("servers", &self.inner.context.servers)
+            .field("best_tcp_idx", &self.inner.context.best_tcp_idx.load(Ordering::Relaxed))
+            .field("best_udp_idx", &self.inner.context.best_udp_idx.load(Ordering::Relaxed))
             .finish()
     }
 }