An i4 molpro build will internally use a signed 32 bit integer to address memory which has a 2GB limit. If you want to address more than that then you'll have to make an i8 build using "configure -i8".
Best wishes, Nick
Gershom (Jan M.L.) Martin wrote:
Greetings:
SHORT VERSUON: Can MOLPRO use more than 2GB of RAM on a P4 or Xeon machine running Linux?
LONG VERSION:
We are running MOLPRO on a cluster of dual Xeon machines running RedHat 8 with updated kernels.
Even on the 4GB machines, the most memory I can get with a stock kernel is -m 253700000 (1936 MB) for a single-CPU job, and -m 194600000 (1485 MB) for a dual-CPU job.
Upon downloading kernel 2.4.24 from kernel.org and applying Andrea Arcangeli's "3.5GB user space" patch
http://ftp.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa1/00_3.5G-address-space-5
I can now get -m 268200000 (2046 MB) in both single-and dual-CPU jobs.
The largest continguous memory segment available is a bit more than 2.5 GB
(due to the obnoxious Linux 7.3/8/9 habit of loading shared object libraries
at the 1 GB mark --- you can see them by 'cat /proc/<processid>/maps) ---
this can be increased a bit further by going to kernel 2.6 with Andrew
Morton's "mm" patches (which include a separate 4GB/4GB user/kernel space patch), and with a lot more doing (somehow forcing the shared object
libraries to load at lower addresses --- ideas anybody?) this can probably
be pushed over the 3 GB mark.
My question is now: is the P4/Linux version of MOLPRO capable at all of handling memory spaces larger than 2GB? Or is this intrinsically off the
menu?
Many thanks in advance Jan Martin -------------------------------------------------------------------- Prof. Gershom (Jan M.L.) Martin Computational Quantum Chemistry Department of Organic Chemistry / Kimmelman Building, Room 252 Weizmann Institute of Science / IL-76100 Rechovot / ISRAEL Email: [EMAIL PROTECTED] Phone: +972(8)9342533 Web site: http://theochem.weizmann.ac.il/ FAX: +972(8)9344142 --------------------------------------------------------------------
