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

[Jeff Hammond]

This is totally platform specific. MPICH on BGQ is different than on
Linux, for example. This question is thus mostly unanswerable. Your
best bet is to consider the POSIX shared memory spec and assume that
MPI uses it.

Jeff

Sent from my iPhone

On Jun 3, 2013, at 3:14 PM, Rolf Rabenseifner <rabenseifner at hlrs.de> wrote:

> 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)
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