OpenJDK and boxes with lots of RAM

[Jan Just Keijser]

David Holmes wrote:
> Hi Jan,
>
> You can use the environment variable _JAVA_OPTIONS to set -Xmx.
>
> The other option is to use your own wrapper script for launching the
> VM that contains whatever flags you need.
>
>
we would really like to avoid a wrapper script. The env var
_JAVA_OPTIONS is a nice workaround, although I'm not thrilled about the
fact that I now see

$ java -version
Picked up _JAVA_OPTIONS: -Xmx256M
java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.10)
(rhel-1.23.1.9.10.el5_7-x86_64)
OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)


Is there any way to get rid of that message?


thx,

JJK / Jan Just Keijser

> On 17/11/2011 11:28 PM, Jan Just Keijser wrote:
>> hi all,
>>
>> I would like to report an issue with OpenJDK 1.6 (and Oracle Java 6u29)
>> that we have run into on our grid computing farm:
>>
>> the latest&greatest worker nodes have 12 cores and 48 GB of RAM ; we
>> offer a maximum 12 jobs slots on these worker nodes, in order to
>> accomodate small and large jobs (users can requests 1 - 12 cores). To
>> ensure that the different jobs don't interfere with each other we also
>> set a VMEM limit for each job slot. The current VMEM limit is 48 / 12 =
>> 4 GB RAM per job slot. Each single core job that starts has a 'ulimit
>> -v' of 4,000,000 .
>>
>> On these boxes OpenJDK 'java' refuses to start:
>>
>> $ java -version
>> Error occurred during initialization of VM
>> Could not reserve enough space for object heap
>> Could not create the Java virtual machine.
>>
>> After some debugging I found that this is caused by the default maximum
>> heap size which java allocates: it scans /proc/meminfo to extrac the
>> amount of RAM installed and divides it by 4 ; an 'strace' shows that
>> indeed 'java' tries to do an 'mmap' call for 12 GB of RAM !
>>
>> A work around is to always specify '-Xmx2GB' or something similar but
>> this does not work for all software that we use , plus , I find it
>> annoying that I have to tell this to all my users.
>>
>> What I would like to see is a system-wide setting for the initial
>> maximum heap size, so that
>>    java -version
>> "just works" . Is this possible?
>>
>> thanks in advance,
>>
>> JJK / Jan Just Keijser
>>
>>