Tomcat memory consumption is more than heap + permgen space

I am observing a mismatch in Tomcat RAM consumption between what the OS says and what jVisualVM says.

From htop, the Tomcat JVM is has 993 MB of resident memory

From jVisualVM, the Tomcat JVM is using

• Heap Max: 1,070,399,488 B


• Heap Size: 298.438.656 B


• Heap Used: variable, between 170MB and and 270MB


• PermGen Max: 268,435,456 B


• PermGen Size: 248,872,960 B


• PermGen Used: slightly variable, around 150MB

From my understanding the OS memory consumption should be Heap Size + PermGen Size ~= 522 MB. But that's 471 MB less than what I'm observing.

Anyone got an idea what am I missing here?

PS: I know that my max heap is much higher than what is used, but I'm assuming that should have no effect if the JVM does not use it (i.e. Heap Size is lower).

Thanks!
Marc

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