[Xen-users] Java JVM and memory on Xen

[Rob Shepherd <rs@xxxxxxxxxxxxx>]

Hi,

I have a strange problem here.

My Java Virtual Machine crashes on a DomU when mem-set is 1792 MB but is 
stable when mem-set has been called with 1791 MB
This happens running JBoss, and is an actual libjvm.so Segfault. It 
doesn't report anything about memory etc.
Running:
very recent quad core Xeon 2Ghz,
Xen 3.1 from OpenSolaris 09/06
OpenSolaris 09/06 Dom0
Ubuntu 8.04 with 2.6.24-25-xen kernel image
JVMs (any... 1.5.0 - 1.7, either openjdk or sun)

I finally tracked down the crash to that single 1MB adjustment of RAM.

although the JVM is only configured to use 512MB of RAM MAX (-Xmx512m)

This is very bizarre.  Has anybody seen behaviour before, or have any 
comments about why it may be happening?
One thought.... Java requires contiguous memory which I believe Xen does 
not provide to the guest. 
I would have thought however that the addressable memory space that an 
application sees can be mapped to appear contiguous?
Thanks for any input, or suggestions

Rob

--
Rob Shepherd BEng PhD - Director / Senior Engineer - DataCymru Ltd



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