[Mpi3-rma] [EXTERNAL] Re: Available size and number of shared memory windows with MPI_WIN_ALLOCATE_SHARED

Barrett, Brian W bwbarre at sandia.gov
Tue Jun 4 10:15:50 CDT 2013

On 6/4/13 4:18 AM, "Jed Brown" <jedbrown at mcs.anl.gov<mailto:jedbrown at mcs.anl.gov>> wrote:

Rolf Rabenseifner <rabenseifner at hlrs.de<mailto:rabenseifner at hlrs.de>> writes:

I would say that the standard is not the right place to document this
sort of thing, but hopefully vendors and computing facilities will
document it prominently because it's an essential consideration for
MPI+MPI.  It would be useful if someone would set up a resource
documenting the hoops one has to jump through on all major platforms.

I think we're still waiting to figure out what those hoops are.   For example, on platforms with XPMEM (Cray XT/XE/XC), the answer is have as many windows that are as big as you can allocate memory for.  On most of the other platforms with Open MPI, it'll be more along the lines of what you could allocate with POSIX shared memory interfaces, which is usually a high number of segments, but the total space is probably limited to a relatively small subset of the total memory (25%?).


  Brian W. Barrett
  Scalable System Software Group
  Sandia National Laboratories
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