[Mpi3-rma] Alternative Proposal for Shared Memory Support

[Torsten Hoefler]

Bronis,

> What happens if the processes do not have shared physical
> memory? 
If the communicator had P processes, then the new window will have P
windows (or groups) with one process in each. 

> Is it just that physical shared memory is used
> when possible? What if multple nodes are included in comm?
Yes, the call is similar to a comm split where all nodes that share a
common memory have the same color and all nodes that don't have
different colors. It will create multiple distinct windows. The user can
query the group to see which processes share a window.

> Will each node use shared memory? That seems fairly
> reasonable. 
Yes, it's basically the same semantics as Ron's original proposal where
a new communicator MPI_COMM_SHM (?) was defined. This functionality will
be assimilated into one call and group query (which is more logical
because one doesn't necessarily need a full communicator). A new use for
groups :-).

> Overall, I think this proposal is good. I do think a number of details
> have to be worked out before it is ready but I agree that discussing
> it at a Forum meeting is the way to go.
Yes, there will be some discussion, but it could be worth it.

> Perhaps we could request a joint RMA/Hybrid WG session to discuss it?
> I think it is a mistake to cover it just within one group or the
> other.
Sure, that would be best. We could also just pick one or the other and
make sure all key people from the both working groups are present ;-).
Seems like less administrative overhead.

Best,
  Torsten

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Torsten Hoefler         | Performance Modeling and Simulation Lead
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