OpenResty 持续运行内存不会回收

使用 OpenResty 运行做压力测试时，发现 OpenResty 占用的内存不会被回收

使用 Systemctl status OpenResty，显示如下：

===========================================================================

● openresty.service - SYSV: OpenResty is a scalable web platform by extending

Loaded: loaded (/etc/rc.d/init.d/openresty; bad; vendor preset: disabled)

Active: active (running) since Sun 2020-05-31 14:00:00 CST; 38min ago

 Docs: man:systemd-sysv-generator(8)

Process: 14643 ExecStart=/etc/rc.d/init.d/openresty start (code=exited, status=0/SUCCESS)

Main PID: 14848 (nginx)

Tasks: 2

Memory: 2.0G

CGroup: /system.slice/openresty.service

       ├─14848 nginx: master process /usr/local/openresty/nginx/sbin/nginx -c /usr/local/openre...
       
       └─24854 nginx: worker process

==========================================================

可以看到已经占用了 2.0G 内存。

请问大家这是什么原因呢？解决方案是什么？？