[mpiwg-rma] MPI_Win_create on unmapped memory?

[Jeff Hammond]

I liked your text, which does not use an platform-oriented terms e.g.
virtual memory language.

Jeff

On Tue, Jan 2, 2018 at 1:59 PM, William Gropp <wgropp at illinois.edu> wrote:

> I see no harm in adding a clarification - not an errata, and not a change.
> Is my text sufficiently precise, or is there better text that we could use?
>
> 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 3:54 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>
> I agree with all of these comments, but a user is arguing that these
> requirements are not clear from the text, e.g. because the meaning of
> existence in "existing memory" is not defined.  It seems that what is
> obvious to us is not obvious to users.
>
> Jeff
>
>
> On Tue, Jan 2, 2018 at 12:54 PM, William Gropp <wgropp at illinois.edu>
> wrote:
>
>> Yes.  The r and l values must remain valid until the free.
>>
>> 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 2:52 PM, Nathan Hjelm <hjelmn at mac.com> wrote:
>>
>> I would expect that the intent is also that the memory should not be
>> freed/unmapped before the matching call to MPI_Win_free() correct?
>>
>> -Nathan
>>
>> On Jan 02, 2018, at 01:19 PM, William Gropp <wgropp at illinois.edu> wrote:
>>
>> 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> 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
>> http://jeffhammond.github.io/
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>
>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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