在swift中,如何在删除SKScene后让内存恢复正常？

当我运行游戏超过十次时,模拟器变得越来越慢并最终崩溃.

在这个简单的游戏中我有两个控制器和一个gamecene：

MainController通过触发按钮调用GameViewController

在GameViewController中,gamescene以这种方式初始化：

class GameViewController: UIViewController
{

  var skView:SKView!

  var scene:GameScene!

  override func viewDidLoad() {

      super.viewDidLoad()
      scene = GameScene(size: view.bounds.size)
      skView = view as SKView
      skView.ignoresSiblingOrder = true
      scene.scaleMode = .ResizeFill

      scene.viewController = self
      skView.presentScene(scene)

  }

//with a prepareForSegue deinitialises the scene and skview:
override func prepareForSegue(segue: UIStoryboardSegue,sender: AnyObject?) {

    if segue.identifier == "GameFinished"{

        scene.removeAllActions()
        scene.removeAllChildren()
        scene.removeFromParent()
        scene = nil

        skView.presentScene(nil)
        skView = nil

        let target = segue.destinationViewController as MainController
    }
  }
}

在GameScene中,viewController是一个属性

var viewController:GameViewController? = GameViewController()

segue被触发：

self.viewController!.performSegueWithIdentifier("GameFinished",sender: nil)

我也试过在GameScene中将remove方法放入deinit：

deinit{
    self.removeAllActions()
    self.removeAllChildren()
  }

仍然行不通