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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: Showing Tomcat Memory Utilization with 'top'
Date Tue, 22 Jun 2010 19:22:49 GMT
> From: Robinson, Eric [mailto:eric.robinson@psmnv.com]
> Subject: Showing Tomcat Memory Utilization with 'top'
> 
> 1. Top shows 0k of swap usage, so the system is not swapping. In that
> case, why is there a difference between the VIRT and RES numbers?

Linux always allocates more virtual space than is actually used (thread stack space, for example).
 The JVM will also reserve, but not commit, the -Xmx size of the heap (and other spaces);
it only commits what is really needed.

> My understanding is that RES=CODE+DATA and VIRT=RES+SWAP.

Nope.  RES is real memory usage, VIRT is just whatever space has been allocated, but not necessarily
touched.  Until a page is touched, it won't exist in RAM or on the swap file.

> 2. Where does the 64MB of java heap show up?

Buried inside the VIRT number.

 - Chuck


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