improve user experience for some users

shadowsocks-csharp/Controller/Service/PACServer.cs

@@ -146,7 +146,7 @@ Connection: Close
 ", System.Text.Encoding.UTF8.GetBytes(pac).Length) + pac;
                 byte[] response = System.Text.Encoding.UTF8.GetBytes(text);
                 socket.BeginSend(response, 0, response.Length, 0, new AsyncCallback(SendCallback), socket);
-                Util.Utils.ReleaseMemory();
+                Util.Utils.ReleaseMemory(true);
             }
             catch (Exception e)
             {

shadowsocks-csharp/Controller/ShadowsocksController.cs

@@ -360,7 +360,7 @@ namespace Shadowsocks.Controller
             }
 
             UpdateSystemProxy();
-            Util.Utils.ReleaseMemory();
+            Util.Utils.ReleaseMemory(true);
         }
 
 
@@ -417,7 +417,7 @@ namespace Shadowsocks.Controller
         {
             while (true)
             {
-                Util.Utils.ReleaseMemory();
+                Util.Utils.ReleaseMemory(false);
                 Thread.Sleep(30 * 1000);
             }
         }