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From Christopher Schultz <>
Subject Re: Showing Tomcat Memory Utilization with 'top'
Date Wed, 23 Jun 2010 17:00:52 GMT
Hash: SHA1


On 6/22/2010 5:00 PM, Caldarale, Charles R wrote:
>> From: Christopher Schultz []
>> Subject: Re: Showing Tomcat Memory Utilization with 'top'
>> Also, I believe VIRT includes memory shared with other processes
> Doesn't RES also include shared pages - anything that's in the memory
> map of the process?  (I can't remember exactly how that works, but
> the shared pages have to be accounted for somewhere.)

This is reaching the limits of my knowledge as well. I could imagine
shared memory not being counted "against" every process but it also
quite makes sense that it would.

>> so if you have 50MiB of Java system classes loaded and a modern 
>> JVM which shares them among running JVMs
> Note that only the client HotSpot JVM shares classes; the server
> version does not.  (The sharing is really class templates, not the
> class objects themselves.)

I didn't realize that the server JVM didn't share class templates. Do
you have any ideas why not? It seems to be a relatively cheap
optimization when multiple JVMs are in use, and shouldn't include too
much overhead for either the process or the OS if there's no actual
sharing going on in a single-JVM scenario.

- -chris
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