Re: [Xen-users] Java JVM and memory on Xen

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Nov 10, 2009 at 01:52:34PM +0000, Rob Shepherd wrote:
> 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
> 

Does domU kernel dmesg have errors?

How does the domU kernel memory layout change when you switch between
1791 and 1792 MB of RAM? (it's in the beginning of dmesg / domU kernel 
boot messages).

Have you tried any other domU kernels? Ubuntu 2.6.24 kernel is known to
be buggy..

-- Pasi


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