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Old 09-08-2008, 04:25 AM   #1
morfeus80
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RAM limitation


Hi guys,

I'm working in a 64bit cluster with 32Gbytes of memory, but I have to run a 32bit software. Therefore I type "setarch i386" to use the cluster like a 32bit PC. The problem now is I can use just 4Mbytes of memory, but I need more.

Is there any chance to allocate more memory?

Thanks!
 
Old 09-08-2008, 04:32 AM   #2
jschiwal
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Are you running SuSE on the cluster? It has a biarch architecture for cpus that run 64 & 32 bit software.
Did you mean 4GB of memory? That is the limit of the x86 architecture, however with the PAE extension you can increase that. This means using a different kernel. I don't think that the program itself can use more than 4GB. The total ram available will increase by increasing the page size.
 
Old 09-08-2008, 04:45 AM   #3
morfeus80
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Thanks jschiwal,

my OS is RedHat. I don't know what PAE is (I'm a Linux newbie)... What could I do to solve my problem? How can I increase the memory limit?
 
Old 09-08-2008, 04:47 AM   #4
syg00
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As stated, you will need a PAE enabled kernel - and motherboard (should be standard these days). And yes, the 32-bit virtual size (per process) is still limited to 4 Gig, regardless of the amount of RAM available.
Quote:
Originally Posted by jschiwal View Post
The total ram available will increase by increasing the page size.
Nope, hugetlb page is something different again.

Update: just saw your latest post; Redhat ship kernels with PAE in the name - just search for and install that. Will probably become the default boot option, else select from the boot menu.

Last edited by syg00; 09-08-2008 at 04:52 AM.
 
Old 09-08-2008, 08:25 AM   #5
johnsfine
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If most of the answers you got so far make any sense, then I've totally misunderstood what you're trying to do. Can you be clearer about that.

Quote:
Originally Posted by morfeus80 View Post
I'm working in a 64bit cluster with 32Gbytes of memory, but I have to run a 32bit software.
The way I interpreted that is you are running a 64-bit Linux on 64-bit hardware, but want to run 32-bit programs within it. Is that correct? Most 64-bit Linux distributions are "multilib" meaning they have no problem running 32-bit programs.

Or did you mean you want to run a completely 32-bit environment (kernel and all programs) on 64-bit hardware? In that case, the "PAE" answers you got are important.

Or do you want to run a 32-bit kernel virtual inside a 64-bit one, or something else stranger than the first two guesses above?

Quote:
Therefore I type "setarch i386"
I looked up what that meant, and if I understood it correctly, it shouldn't be necessary nor even helpful for any of what I think you might be trying to do. In a 64-bit multilib system, you should be able run 32-bit programs by just running them.

Quote:
The problem now is I can use just 4Mbytes of memory, but I need more.
We assume you mean 4GB not 4MB. But 4GB per what?

The limit of 4GB per process (when running 32-bit programs under a 64-bit OS) is forced by the architecture. You aren't going to get around it. If the 32-bit program were running under a 32-bit kernel you'd have just 3GB per process.

But if you just want a total over 4GB (multiple processes of under 4GB each, adding up to over 4GB) that's easy. With a 64-bit kernel or a 32-bit PAE kernel, it just works that way.

Last edited by johnsfine; 09-08-2008 at 08:28 AM.
 
Old 09-08-2008, 08:58 AM   #6
morfeus80
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Hi johnsfine,

Quote:
The way I interpreted that is you are running a 64-bit Linux on 64-bit hardware, but want to run 32-bit programs within it. Is that correct? Most 64-bit Linux distributions are "multilib" meaning they have no problem running 32-bit programs.
this is correct! But if I run the program without typing"setarch i386", it doesn't work.

From you answer I understand I haven't any chance to increase the memory.
 
Old 09-08-2008, 09:52 AM   #7
johnsfine
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Quote:
Originally Posted by morfeus80 View Post
From you answer I understand I haven't any chance to increase the memory.
From any of the answers above you can understand you haven't any chance to increase the memory per 32-bit process.

I'm curious what program you're trying to run. If it's open source, you could recompile it for 64-bit mode. If it's anything commonly used then posting what it is would make you more likely to get some constructive advice on how to deal with the 4GB limit.
 
  


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