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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 19:55:32 GMT
> From: Robinson, Eric [mailto:eric.robinson@psmnv.com]
> Subject: RE: Showing Tomcat Memory Utilization with 'top'
> 
> For example, I have a tomcat configured to use 96MB of heap (export
> JAVA_OPTS="-ms96M -mx96M"). Top shows VIRT=336396, RES=227264. I'm
> guessing that the 96MB of heap is buried in BOTH the VIRT and RES
> numbers?

Since -Xms == -Xmx, that is normally true.  However, the JVM may not have actually used all
the allocated heap space, since the heap is internally divided into several regions (eg, eden,
survivor, tenured), and some of these are further subdivided (TLAB).  If a page in the heap
hasn't been touched (not unusual for some TLAB areas), it will appear in VIRT but not in RES.

 - Chuck


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