the memory usage of hotspot vm itself

[Li Li]

    I have an application running in a machine with 6 GB memory. And the
java program is allocated to use 4000M heap by -Xmx4000m and -Xms4000m. But
we found it use swap memory and system get slower.
When swapping, the total memory used by the java process is 4.6GB(use top
res 4.6G and virt 5.1G)
   I know Direct Buffer used by NIO, PermGen and stack is not limited by
Xmx. we limit stack 256k and 400 threads in peak. so it will use 80MB
memory and MaxPermSize is 256MB. MaxDirectMemorySize is default. I think is
64MB
all sumed up is about 3400MB. so JVM itself will need more than 200MB.
   any one tell me why JVM need more than 200MB memory?(I don't mean jvm
should not use that much memory). how could I estimate the memory usage of
JVM itself? thanks.
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