use make slice to store objects to improve efficiency

Signed-off-by: allencloud <allen.sun@daocloud.io>

pkg/kubelet/dockershim/docker_container.go

@@ -350,7 +350,7 @@ func (ds *dockerService) ContainerStatus(containerID string) (*runtimeapi.Contai
 	imageID := toPullableImageID(r.Image, ir)
 
 	// Convert the mounts.
-	mounts := []*runtimeapi.Mount{}
+	mounts := make([]*runtimeapi.Mount, 0, len(r.Mounts))
 	for i := range r.Mounts {
 		m := r.Mounts[i]
 		readonly := !m.RW

pkg/kubelet/dockershim/docker_image.go

@@ -40,7 +40,7 @@ func (ds *dockerService) ListImages(filter *runtimeapi.ImageFilter) ([]*runtimea
 		return nil, err
 	}
 
-	result := []*runtimeapi.Image{}
+	result := make([]*runtimeapi.Image, 0, len(images))
 	for _, i := range images {
 		apiImage, err := imageToRuntimeAPIImage(&i)
 		if err != nil {

pkg/kubelet/dockershim/docker_legacy.go

@@ -187,7 +187,7 @@ func (ds *dockerService) ListLegacyPodSandbox(filter *runtimeapi.PodSandboxFilte
 	}
 
 	// Convert docker containers to runtime api sandboxes.
-	result := []*runtimeapi.PodSandbox{}
+	result := make([]*runtimeapi.PodSandbox, 0, len(containers))
 	for i := range containers {
 		c := containers[i]
 		// Skip new containers with containerTypeLabelKey label.
@@ -242,7 +242,7 @@ func (ds *dockerService) ListLegacyContainers(filter *runtimeapi.ContainerFilter
 	}
 
 	// Convert docker to runtime api containers.
-	result := []*runtimeapi.Container{}
+	result := make([]*runtimeapi.Container, 0, len(containers))
 	for i := range containers {
 		c := containers[i]
 		// Skip new containers with containerTypeLabelKey label.

pkg/kubelet/dockershim/docker_service.go

@@ -335,7 +335,7 @@ func (ds *dockerService) GetPodPortMappings(podSandboxID string) ([]*hostport.Po
 		}
 	}
 
-	portMappings := []*hostport.PortMapping{}
+	portMappings := make([]*hostport.PortMapping, 0, len(checkpoint.Data.PortMappings))
 	for _, pm := range checkpoint.Data.PortMappings {
 		proto := toAPIProtocol(*pm.Protocol)
 		portMappings = append(portMappings, &hostport.PortMapping{

pkg/kubelet/dockershim/helpers.go

@@ -127,7 +127,8 @@ func extractLabels(input map[string]string) (map[string]string, map[string]strin
 // '<HostPath>:<ContainerPath>:ro', if the path is read only, or
 // '<HostPath>:<ContainerPath>:Z', if the volume requires SELinux
 // relabeling and the pod provides an SELinux label
-func generateMountBindings(mounts []*runtimeapi.Mount) (result []string) {
+func generateMountBindings(mounts []*runtimeapi.Mount) []string {
+	result := make([]string, 0, len(mounts))
 	for _, m := range mounts {
 		bind := fmt.Sprintf("%s:%s", m.HostPath, m.ContainerPath)
 		readOnly := m.Readonly
@@ -147,7 +148,7 @@ func generateMountBindings(mounts []*runtimeapi.Mount) (result []string) {
 		}
 		result = append(result, bind)
 	}
-	return
+	return result
 }
 
 func makePortsAndBindings(pm []*runtimeapi.PortMapping) (map[dockernat.Port]struct{}, map[dockernat.Port][]dockernat.PortBinding) {