Please keep us informed as to what you discover, Marcy. I am sure others
could benefit from your efforts.
Marcy Cortes wrote:
I was wrong. There is one JVM and 3 apps in that.
But we're seeing it on those that just have 1 app per JVM as well.
I appears some changes that went in last night may have changed the behavior
-- a bit too early to tell, more time and testing required there. FP 11 +
Generational garbage collection (which also saves it looks like 13% CPU as
well).
Marcy Cortes
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-----Original Message-----
From: Linux on 390 Port [mailto:[EMAIL PROTECTED] On Behalf Of Dave
Jones
Sent: Monday, October 22, 2007 9:06 PM
To: [email protected]
Subject: Re: [LINUX-390] Another Linux swapping question
Well, my colleague Rob v.d. Heij beat me to the punch line, but this was
where I was headed....having more than one JVM inside a Linux guest is,
imho, asking for trouble. Is there a reason you need to have multiple JVMs
running at the same time?
Rob van der Heij wrote:
On 10/22/07, Marcy Cortes <[EMAIL PROTECTED]> wrote:
Why would a server show such a high amount in cached when it is
needing to swap?
In your case, it's probably the JVM heap that is resisting. The JVM
does its own management of the heap. Just like in real life: when you
have multiple managers, you want at most one of them to actually do
something ;-) Once the heap has been given to the JVM, Linux memory
management can not see inside. When Linux cannot manage it, you want
the heap to be resident in the virtual machine.
But one can and should question whether the JVM heap is properly
sized. Some of the rules of thumb in sizing the heap (like "when in
doubt, double it") come from the world of spare memory and may not
apply to Linux on z/VM. The Java Garbage Collector is not as scary as
it used to be. There's options in GC to see high water marks etc that
help you size the heap. I have seen installations so oversize that
after weeks the first GC had not even happened. If you can make it
clean up now and then, you limit the amount of fresh pages and have
more chance to keep those pages resident on VM. That may very well
outweigh the extra cost for GC now and then.
Rob
--
Rob van der Heij
Velocity Software, Inc
http://velocitysoftware.com/
--
DJ
V/Soft
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DJ
V/Soft
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