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Old 03-08-2004, 02:14 PM   #1
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Maximum Memory PER PROCESS

I've been trying to clarify how much memory per process is available using Linux and 64bit processors like the Opteron or the Itanium2. Even if Linux supports 64Gb or RAM, if you've got apps that need more than 3GB per process and you're on x86, then you're out of luck. I've got some such applications, that require more than 3GB per process. So I'm currently "out of luck". It doesn't matter that my machines have 8Gb+ ram. 3GB per process is the max on these x86 boxes.

I've gotten my hands on an Itanium2 box, and I'm currently waiting for 8GB of RAM to arrive. Soon I will know the answer, but in the meantime I am trying to find out from anyone who knows for sure, whether or not 64bit processors raise the bar on maximum memory "per process" and allow processes to use more than the 3GB per process max.

Can I stick with 2.4 kernel and my Itanium2 or Opteron box, or do I need to use 2.6 to get beyond the 3GB per process max?

The closest answer I've gotten so far was from a guy named John-Paul Stewart, who demanded I look at TASK_SIZE in /usr/src/linux/include/asm-x86_64/processor.h instead of just telling me how much memory per process was supported.

Hint: I'm not entirely sure what the TASK_SIZE is supposed to represent, so I still do not know that answer to my question - "How much memory per process is allowed with kernel 2.4 running on Itanium2 processor".
Old 03-08-2004, 03:29 PM   #2
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When you configure a kernel for compiling 32 bit, you have to option to turn on "High Memory" support. This has been available for a while (and is available for, at least, the 2.4.21 kernel). I would suggest you turn on the 64GB support for high memory (this should allow the Linux kernel to address all of your memory). This applies to 32 bit CPUs.
64 bit CPUs have a physical memory limit of about 1TB, so your 8GB RAM will all be addressable. The per process size limit also is going to be much larger than the 8GB you are talking about.
If you are running 32 bit processes, though, you're still stuck with the 32 bit addressable space, which is about 3-4 GB, even if you've got a 64 bit kernel. . .

Last edited by moses; 03-08-2004 at 03:32 PM.


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