为什么我的java进程使用了内存(Linux RES) ?

I have a java(1.6 u25) process running on linux(centos 6.3 x64) with JAVA_OPTS="-server -Xms128M -Xmx256M -Xss256K -XX:PermSize=32M -XX:MaxPermSize=32M -XX:MaxDirectMemorySize=128M -XX:+UseAdaptiveSizePolicy -XX:MaxDirectMemorySize=128M -XX:+UseParallelGC -XX:+UseParallelOldGC -XX:GCTimeRatio=39 -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:gc.log", the java app used thrift 0.8.0 lib;I have a java(1.6 u25) process running on l