https://blog.faceutil.com/2017/03/25/%eb%a9%94%eb%aa%a8%eb%a6%ac-%ec%b5%9c%ec%a0%81%ed%99%94-%ed%94%84%eb%a1%9c%ea%b7%b8%eb%9e%a8-%ed%81%b4%eb%a6%b0%eb%a9%a4cleanmem-%e3%81%a2/