java process memory usage is higher than Xmx

[yao]

Hi All,

I have a java process (HBase region server process ) running under Java 7
(1.7.0_40-b43) with G1 enabled. Both Xms and Xmx are the same. After
running process for a few hours, I see the actual memory used by the
process is about 10 percent higher than given Xmx. Has anyone experienced
the similar when use Java 7 or G1 ? Is there useful tools to diagnose the
cause ?

I've tried jmap but the output doesn't say anything about high memory
usage. FYI, the java process use a large heap (90GB), but the actual memory
usage ($ top) is about 99GB.

Thanks
Shengzhe
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