pmap confuse java applicaiton memeory used

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在SUSE中，当用pmap 查看 java 进程时，会看到很多信息

> pmap 32088
32088: java
START               SIZE     RSS     PSS   DIRTY    SWAP PERM MAPPING
0000000040000000     36K     36K      1K      0K      0K r-xp /usr/java/jdk1.6.0_31/bin/java
0000000040108000      8K      8K      8K      8K      0K rwxp /usr/java/jdk1.6.0_31/bin/java
000000004010a000   2492K   2448K   2448K   2448K      0K rwxp [heap]
0000000683600000 23104K 11276K 11276K 11276K      0K rwxp [anon]
0000000684c90000   1728K      0K      0K      0K      0K ---p [anon]

..............................................

00007fff26dd6000      4K      4K      0K      0K      0K r-xp [vdso]
ffffffffff600000      4K      0K      0K      0K      0K r-xp [vsyscall]
Total:           6594996K 82020K 73089K 72296K      0K

6382660K writable-private, 209860K readonly-private, 2476K shared, and 82016K referenced

“writeable/private” 是包括虚拟内存，公共lib等的进程消耗，对于Java进程无参考意义，the RSS(物理内存)是要关注的。

注意：该值不只是heap

The memory usage for the java process is more that just the Java heap. It consists of (hope it didn't forget anything):

the Java heap (where allocated objects go)

the permgen (where static class data goes)

the thread stacks (where method-local references, basic data values, and other information used to maintain method calling go)

various other C/C++ data structures used by the JVM to do its job

the binary code for the JVM and the libraries that it uses to do it job

the binary, compiled code for the Java methods

这些命令也是非常有用的：
jstat -gc PID

top -p PID

ps -uf -p PID

jstack PID

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