process memory limitations

[Jonathan Berry]

On 1/22/06, Oded Maimon <oded.maimon at gmail.com> wrote:
> Hi,
>
> I've a question about per process memory allocation limitation.

You do realize this is a list for Fedora, not RHEL, right?  Please
point other RHEL questions to the RHEL list.  You will get more/better
help there.

> if i've a 32bit machine, with RHEL 4, what are the limitation of memory
> that each process can allocate?

That depends on if your kernel has the 4G/4G patch or not.  I think
that patch floated in and out of the Fedora kernels for a while there.
 Anyway, if you do it is 4 GB.  Otherwise, I believe the split is 3 GB
user 1 GB kernel, so 3 GB.

> if i've a 64bit machine, with RHEL 4, and i'm using a 32bit program,
> what are the limitation of memory that each process can allocate?

That's an interesting question and I'm not sure.  But after thinking
about it, pointers in a 32-bit program are, well, 32-bits wide.  So I
don't see how it could possibly address more than 32-bits worth of
space.  So my guess would be 4 GB again.  Now, a 64-bit program has a
whole lot more.  I don't remember how much, but I doubt the exact
number is relevant, as it is probably more space than any normal
computer could handle : ).

Also, these are address space limitations.  The limitation on the
amount of memory a process can allocate depends also on the size of
the text and stack needed.  ulimit may also be able to impose some
limit as well, though I'm not familiar with all of its capabilities.

Jonathan