[molpro-user] Shared memory

John Sears gtg390f at mail.gatech.edu
Wed Nov 9 17:08:01 GMT 2005

Dear users,
How does one limit the size of the shared memory segments in molpro?  I was
trying to run a rather large caspt2 calculation on two dual-processor Xeon
boxes.  The program ignores the -G option, printing this fact in the output

" ga_uses_ma=false, calling ma_init with nominal heap. Any -G option will be

The initial parts of the calculation runs fine, until getting the CASSCF.
This CASSCF is able to run fine on a single node,but when trying to run
across two nodes I get the following ARMCI error.

******************* ARMCI INFO ************************
The application attempted to allocate a shared memory segment of 5595660288
bytes in size. This might be in addition to segments that were allocated
succesfully previously. The current system configuration does not allow
enough shared memory to be allocated to the application.
This is most often caused by:
1) system parameter SHMMAX (largest shared memory segment) being too small
2) insufficient swap space.
Please ask your system administrator to verify if SHMMAX matches the amount
of memory needed by your application and the system has sufficient amount of
swap space. Most UNIX systems can be easily reconfigured to allow larger
shared memory segments,
see http://www.emsl.pnl.gov:2080/docs/global/support.html
In some cases, the problem might be caused by insufficient swap space.
0:allocate: failed to create shared region : -1

The SHMMAX on these nodes is set to 6.5 GB.  The nodes only have 8GB of
memory each, so increasing SHMMAX much more than the current setting may be
dangerous.  How can I limit the size of the shared memory segment?  Does the
size of the shared memory segment count against the per-process memory
specified with -m ?  Any help greatly appreciated.
Best wishes

John Steven Sears
Center for Computational Molecular Science and Technology
School of Chemistry and Biochemistry
Georgia Institute of Technology
Atlanta, GA 30332-0400
Office: Boggs 3-19
Phone: 404-385-1310
email: john.sears at chemistry.gatech.edu

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