https://blog.wongcw.com/2019/01/28/centos%e6%9b%b4%e6%96%b0%e8%bb%9f%e4%bb%b6%e5%8c%85%e6%8f%90%e7%a4%bacannot-allocate-memory%e9%8c%af%e8%aa%a4%e8%88%87%e8%a7%a3%e6%b1%ba/