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

[Rob Shepherd <rs@xxxxxxxxxxxxx>]

Update:

It works fine with Oracle/BEA's JRockit VM, which according to a google 
can operate with a non-contiguous heap.
Is heap (memory allocation) coniguity a problem for Xen?

Many thanks

Rob

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

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