Karl Misselt wrote:
> Hi All - A simple question I think I know the answer to, but want
> confirmation on before buying hardware.  I need to buy a workstation
> for processing very large format array data, so we'd like to have
> a fair amount of RAM on the machine.  SL4.0 has the capability to
> handle up to 64GB of physical RAM, correct?  We're planning on putting
> 4-6GB on this machine, which brings me to the second question.  As I
> understand, even with 6GB of RAM, a single process will only be able
> to access <4GB of RAM, assuming a 32-bit architecture.  On a 64-bit
> machine, more RAM would be available to a single process - does anyone
> know what the number is?  And further, how much of the 6GB would be
> paged to the kernel in SL4?  Thanks for any info!
> -Karl

Hi Karl,
You want to read the release notes.

ftp://ftp.scientificlinux.org/linux/scientific/40/i386/SL.documentation/RELEASE-NOTES-x86-en

Particularly this part

      o Scientific Linux 4.0 includes a kernel known as the hugemem
kernel. This kernel supports a 4GB per-process user space (versus 3GB
for the other kernels), and a 4GB direct kernel space. Using this
kernel allows Scientific Linux to run on systems with up to
64GB of main memory. The hugemem kernel is required in order to use
all the memory in system configurations containing more than 16GB of
memory. The hugemem kernel can also benefit configurations running
with less memory (if running an application that could benefit from
the larger per-process user space, for example.)

   Note

To provide a 4GB address space for both kernel and user space, the
kernel must maintain two separate virtual memory address mappings.
This introduces overhead when transferring from user to kernel space;
for example, in the case of system calls and interrupts. The impact of
this overhead on overall performance is highly application dependent.


Troy

-- 
__________________________________________________
Troy Dawson  [log in to unmask]  (630)840-6468
Fermilab  ComputingDivision/CSS  CSI Group
__________________________________________________