[Mpi3-rma] Draft Plenary Presentation for MPI RMA

Torsten Hoefler htor at illinois.edu
Fri Feb 4 15:11:37 CST 2011

On Fri, Feb 04, 2011 at 02:45:42PM -0600, James Dinan wrote:
> Hi Torsten,
> On 02/04/2011 12:35 PM, Torsten Hoefler wrote:
>>> Slide 22: UPC doesn't allow sharing data on the stack, only heap data
>>> can be shared.  In general, this is kind of an iffy thing, might
>>> encounter some resistance to suggest doing this.  Linux is going to
>>> initially map the stack to the zero page which is marked copy-on-write,
>>> so beyond the parts you have used, the stack doesn't exist.
> >
>> That's what registration is for. It has to be created then. Or am I
>> missing something?
> UPC doesn't allow shared variables on the stack and I can't think of any  
> other PGAS model that does.  So, the argument of registering and  
> exposing the stack doesn't seem like it holds water to me.
Well, the current proposal allows this. One can register anything that
can be dereferenced, including stack variables. If you think that should
not be allowed than we need to fix the proposal. The slides simply
explain the proposal.

> I believe Dan, et al.'s issue with MPI_Alloc_mem as a requirement is  
> that *static* shared UPC objects could not be put into windows.  Static  
> distributed shared arrays are one of the most common use cases in UPC.  
> Adding win_register now allows you to register statically declared  
> arrays and expose them in a window.
This is allowed too. 


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Torsten Hoefler         | Performance Modeling and Simulation Lead
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