内存 180M，选装了 debian，外加 wordpress、sshd、mysql、nginx。500
并发数持续测试 5 分钟
137% webbench -c 500 -t 300 http://127.0.0.1/
Webbench - Simple Web Benchmark 1.5
Copyright (c) Radim Kolar 1997-2004, GPL Open Source Software.
Benchmarking: GET http://127.0.0.1/
500 clients, running 300 sec.
Speed=1446 pages/min, 522264 bytes/sec.
Requests: 7232 susceed, 0 failed.
138% free -m
total used free shared buffers cached
Mem: 180 130 50 0 5 69
-/+ buffers/cache: 55 125
Swap: 191 0 191