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

Jed Brown jedbrown at mcs.anl.gov
Tue Jun 4 06:18:21 CDT 2013

Rolf Rabenseifner <rabenseifner at hlrs.de> writes:

> In principle, to stay within one programming model is attractive.
> Therefore, I want to learn what are the limits of MPI_WIN_ALLOCATE_SHARED.

As Jeff says, it's more about the operating system.  The MPI standard
does not specify whether environment steps will be necessary in order to
use MPI_Win_allocate_shared.  On a system without virtual memory (like
CNK on BG/Q), you have to reserve a chunk of address space when the node
is booted.  In these environments, you need contiguous physical memory
in order to address it contiguously, as provided by

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.

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