https://blog.faceutil.com/2017/03/27/%eb%a9%94%eb%aa%a8%eb%a6%ac-%ec%b5%9c%ec%a0%81%ed%99%94-%ec%9c%a0%ed%8b%b8%eb%a6%ac%ed%8b%b0-cleanmem-%e3%8e%b5/