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Old 01-06-2009, 03:47 PM   #1
daab
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Question can a 32-bit java app access 2^64 on a 64-bit linux OS?


I'm currently running a large JVM application on a 32-bit RHEL AS 4 update 4 running on 64-bit hardware. Right now, I believe this application can theoretically access 2^32 bits of Virtual Memory (VM).

First question, what is the actual VM a process in 32-bit linux can access? (is it different for different distros?)

The main question... Is it possible for this JVM application to run as-is (compiled 32-bit, using 32-bit JVM) on a 64-bit Linux OS and access more than the theoretical 2^32 (the 2^64)?

If not, would I only need to change to a 64-bit JVM or would I also be required to recompile my 32-bit app using a 64-bit JDK in order to access the 2^64 bit VM?

Just some background:
The main issue is that even though the application itself is not using up all of the java heap allocated to it during start up, deploying this J2EE application into the JVM-based container is failing as I get a non-permgen, non-heap, out of memory native exception related to java's zip utility. The odd part is that lowering heap allocated to this application allows the deployment to go through; suggesting that the zip util is using VM outside the JVM allocated heap, but limited to some limit based on the 2^32 rule. So that is why I am wondering if a 64-bit OS would help.

Thanks.

Last edited by daab; 01-06-2009 at 03:50 PM.
 
Old 01-06-2009, 03:55 PM   #2
Alien Bob
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The java-compiled bytecode does not care if your JVM is 32bit or 64bit. The identical binary will run on both.

Eric.
 
Old 01-06-2009, 04:05 PM   #3
daab
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But will a 32-bit JVM itself be able to address a 64-bit virtual memory? I'm not sure how translation works. This thread seems to say no: http://kerneltrap.org/node/6617
 
Old 01-06-2009, 04:09 PM   #4
Alien Bob
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No, that is why you want a 64bit OS as well as a 64bit JVM...

Eric
 
Old 01-06-2009, 04:12 PM   #5
daab
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Oh, ok. So just to confirm, as long as the JVM is 64-bit, it doesn't matter on what JDK (32/64) you produced bytecode, you're app running inside of the 64-bit JVM will be able to utilize the 64 bit VM?
 
  


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