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64Bit JVM on a 32Bit Gentoo using PAE?
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commander-keen
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Joined: 09 Oct 2013
Posts: 47
Location: Europe

PostPosted: Wed Sep 24, 2014 4:25 pm    Post subject: 64Bit JVM on a 32Bit Gentoo using PAE? Reply with quote

Hi,

not quite sure if this is the right place for my question, but here's the thing.:
I am currently involved in a scientific java based project that has to deal with "a lot" of data. Recently I am facing the problem that the model is exceeding the JVM's maximum assignable heap space ( = RAM available vor the JVM). However the project is executed by a 32Bit JVM and I read this barrier (about 4GB) can be sidestepped by using a 64bit JVM. [The affected machines could be upgraded to an amount of 8GB, physical]

So what I am wondering now is what are the presuppositions to switch to a 64Bit JVM. Will it
*A) work with a 32Bit kernel if Physical Address Extension for RAM > 4GB is kernel-enabled.
*B) suffice to recompile the kernel as 64bit.
*C) be unevitable to set up a new Gentoo installation based on the AMD64 architecture (which I don't hope, for I am happy with my OS as it is now and some of my machines don't support the x86_64 instruction set).

Thanks in advance,
Max
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krinn
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Joined: 02 May 2003
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PostPosted: Wed Sep 24, 2014 7:51 pm    Post subject: Reply with quote

A) yes and no : PAE remove the limit to use more than 4G of ram, but not the limit to access more than 4G. So you can use applications that would eat 8G of ram, as long as applications aren't themselves trying to handle more than 4G.
Still of course, you cannot run it 64bits but must keep using the 32bits version (a limit that itself should limit the application to 4G only).
B) no, you need a full 64bits toolchain
C) see B

Alas for you i think option C looks only the saner choice.
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commander-keen
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Joined: 09 Oct 2013
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PostPosted: Wed Sep 24, 2014 9:47 pm    Post subject: Reply with quote

Thanks for the quick and helpful response, Krinn!
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