nginx worker process exited on signal 9

进行长连接压力测试，测试过程中发现已建立的连接断开，
查看logs/error.log中有
2014/02/21 13:54:33 [alert] 389#0: worker process 390 exited on signal 9
2014/02/21 14:17:06 [alert] 3352#0: worker process 3355 exited on signal 9


查看内核信息（dmesg）:
Out of memory: Killed process 3355 (nginx).
系统内存不可用导致进程挂掉。