diff --git a/app/proxyman/inbound/worker.go b/app/proxyman/inbound/worker.go
index 13ef405f..2a2793eb 100644
--- a/app/proxyman/inbound/worker.go
+++ b/app/proxyman/inbound/worker.go
@@ -187,15 +187,6 @@ func (c *udpConn) Write(buf []byte) (int, error) {
 	return n, err
 }
 
-// Implements buf.ActivityNotifiable
-func (c *udpConn) NotifyActivity() error {
-	if c.done.Done() {
-		return newError("connection is already closed")
-	}
-	c.updateActivity()
-	return nil
-}
-
 func (c *udpConn) Close() error {
 	common.Must(c.done.Close())
 	common.Must(common.Close(c.writer))
diff --git a/common/buf/copy.go b/common/buf/copy.go
index c1721eb5..87a9518e 100644
--- a/common/buf/copy.go
+++ b/common/buf/copy.go
@@ -8,11 +8,6 @@ import (
 	"v2ray.com/core/common/signal"
 )
 
-// ActivityNotifiable is a object that accepts activity notification outside the object
-type ActivityNotifiable interface {
-	NotifyActivity() error
-}
-
 type dataHandler func(MultiBuffer)
 
 type copyHandler struct {
@@ -36,15 +31,6 @@ func UpdateActivity(timer signal.ActivityUpdater) CopyOption {
 	}
 }
 
-// NotifyActivity is a CopyOption to notify activity on each data copy operation.
-func NotifyActivity(notifier ActivityNotifiable) CopyOption {
-	return func(handler *copyHandler) {
-		handler.onData = append(handler.onData, func(MultiBuffer) {
-			notifier.NotifyActivity()
-		})
-	}
-}
-
 // CountSize is a CopyOption that sums the total size of data copied into the given SizeCounter.
 func CountSize(sc *SizeCounter) CopyOption {
 	return func(handler *copyHandler) {
diff --git a/proxy/dokodemo/dokodemo.go b/proxy/dokodemo/dokodemo.go
index 46bfd668..22758505 100644
--- a/proxy/dokodemo/dokodemo.go
+++ b/proxy/dokodemo/dokodemo.go
@@ -164,10 +164,6 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn in
 
 			writer = &buf.SequentialWriter{Writer: tConn}
 			tReader := buf.NewPacketReader(tConn)
-			notify, ok := conn.(buf.ActivityNotifiable)
-			if !ok {
-				panic("conn should implement ActivityNotifiable")
-			}
 			requestCount++
 			tproxyRequest = func() error {
 				defer func() {
@@ -175,7 +171,7 @@ func (d *DokodemoDoor) Process(ctx context.Context, network net.Network, conn in
 						timer.SetTimeout(plcy.Timeouts.DownlinkOnly)
 					}
 				}()
-				if err := buf.Copy(tReader, link.Writer, buf.UpdateActivity(timer), buf.NotifyActivity(notify)); err != nil {
+				if err := buf.Copy(tReader, link.Writer, buf.UpdateActivity(timer)); err != nil {
 					return newError("failed to transport request (TPROXY conn)").Base(err)
 				}
 				return nil