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[Xen-users] Java memory allocation in guest domain with mem and max-mem

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Subject: [Xen-users] Java memory allocation in guest domain with mem and max-mem properties
From: "Roberto Lo Giacco" <rlogiacco@xxxxxxxxxxxx>
Date: Thu, 17 Jul 2008 18:28:58 +0200
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Hi, I've tried to search the list archives but I didn't found anything
about this and I'm experiencing some problems I need to solve quickly
so here follows my question and related doubts.

* The configuration

I've an 8GB equipped with 2 dual core xeon cpus server running CentOS
5.1 (x64) and xen 3.0.3-41.el5 on kernel 2.6.18-53

I'm running 4 DomU each one with mem = 512M and max-mem=2GB

Each of my DomU runs a java application (JBoss 4.2.2-GA) using the Sun
JDK with options to grow java heap size from 256M to 1G on

* The problem

My JVM runs out of memory without balloing the Xen memory, or at least
this is what I think I'm experiencing.

If I run free in the DomU or xm top in the Dom0 I see my DomUs memory
standing still at 512M, if I run top in the DomU I see the java
process running with 300M on memory and 700M on swap space (which is
something I want to avoid and let the app run in memory) and in some
occasions going in OutOfMemoryError without seeing the xen memory
balloing out

* The question

Have I missed something (I'm quite new to xen) in my configuration
files, like using mem-min and mem-max instead of mem and mem-max?
Anyone out there has already encountered this behavior and solved it?
Does this error depends on the used JVM or is there any solution which
is not just "set your DomU memory to a fixed value of 2GB" (btw, this
is the only solution which comes to me)?

Thank you in advance for your patience guys (and ladies, if any!)

   Roberto Lo Giacco

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