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!

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.

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?

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.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.

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.

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?

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.

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.

Hi johnsfine,

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.

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.