asp.net 累加 写入txt文件

string m_LogName = Server.MapPath("logServer.txt");
        if (!System.IO.File.Exists(m_LogName))
        {

            System.IO.FileStream fsnew = System.IO.File.Create(m_LogName);
            fsnew.Close();
        }         
        using (System.IO.FileStream fs = System.IO.File.Open(m_LogName, System.IO.FileMode.Append, System.IO.FileAccess.Write))
        {
            using (System.IO.StreamWriter w = new System.IO.StreamWriter(fs))
            {
                w.WriteLine("记录时间:{0}", DateTime.Now.ToString());
                w.WriteLine("用户ID:{0}", "11");
                w.WriteLine("用户名称:{0}", "22");
                w.WriteLine("IP地址:{0}", Request.UserHostAddress);
                w.WriteLine("MAC地址:{0}", GetCustomerMac(Request.UserHostAddress));
                w.WriteLine("上传文件路径:{0}",Request.Url.ToString());
                w.WriteLine("---------------------------------------------------------------------------------------------");
                w.Flush();
                w.Close();
            }
        }