[mpiwg-rma] MPI_Win_create on unmapped memory?

[Underwood, Keith D]

That limitation is why MPI_WIN_CREATE_DYNAMIC was created…

From: mpiwg-rma [mailto:mpiwg-rma-bounces at lists.mpi-forum.org] On Behalf Of William Gropp
Sent: Tuesday, January 02, 2018 3:19 PM
To: MPI WG Remote Memory Access working group <mpiwg-rma at lists.mpi-forum.org>
Cc: MPI WG Remote Memory Access working group <mpiwg-rma at mpi-forum.org>
Subject: Re: [mpiwg-rma] MPI_Win_create on unmapped memory?

It was certainly the intent that the memory be allocated.  Specifically, if a is the pointer and the region is of length L, then (assuming char *a and ) a[0] … a[L-1] must be valid r and l values at the point of the call.

Bill

William Gropp
Director and Chief Scientist, NCSA
Thomas M. Siebel Chair in Computer Science
University of Illinois Urbana-Champaign





On Jan 2, 2018, at 1:52 PM, Jeff Hammond <jeff.science at gmail.com<mailto:jeff.science at gmail.com>> wrote:

If a user passes a (base,size) pair that corresponds to a range of addresses that are not allocated and/or mapped, is that a correct MPI program?

The only text I can find that implies that buffers passed to MPI_Win_create have to be allocated is the following, assuming that one interprets "existing memory" this way.

"Each process specifies a window of existing memory that it exposes to RMA accesses by the processes in the group of comm." (MPI 3.1 11.2.1)

The Fortran-specific text is similarly suggestive, but it only says that a user can pass a simply contiguous array, not that such a thing is required.

"In Fortran, one can pass the first element of a memory region or a whole array, which must be ‘simply contiguous’"

Thanks,

Jeff

--
Jeff Hammond
jeff.science at gmail.com<mailto:jeff.science at gmail.com>
http://jeffhammond.github.io/
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