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

[Rolf Rabenseifner]

Dear implementers of MPI-3.0 MPI_WIN_ALLOCATE_SHARED,

my question is not about the Interface, but on the implementations:

If a set of MPI processes within a shared memory node and Communicator
wants to allocate a shared memory window:

 - Are there similar limits as if a set of threads wants to allocate
   memory and use it as global Memory by all threads, i.e.,
   is it possible to allocate most physical 
   memory with MPI_WIN_ALLOCATE_SHARED?

 - Is there an additional restriction on the number of shared memory
   windows?

 - Is there an additional restriction if one process defines the 
   whole size as window size and all other processes within 
   the SMP node use size=0?

 - Do you know other restrictions if I want to substitute 
   OpenMP (not OpenMPI!) by shared memory MPI programming,
   i.e. hybrid MPI+MPI instead of hybrid MPI+OpenMP?

Is your answer generally valid for mpich and OpenMPI and must 
I expect some additional restrictions on some vendor's MPIs?

It is about the real implementations, e.g. in mpich and OpenMPI,
but I expect that our MPI-3 RMA working group knows the answer.

Best regards
Rolf


-- 
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)