[mpich-devel] tackling "large datatype" change

[Rob Latham]

I've been trying to tackle tt #1742, #1890, and #1893 as part of some
I/O work that uses large datatypes.

Am I stepping on anyone's toes here?  Pavan, I know i bugged you about these
tickets.  Hope I didn't waste my Thursday on this...

Pavan told me there are two problems here, but I think there are
really one solution to both:

- large datatype means a datatype that describes more than 2 gigs of
  data.  A million contigs of a million contigs, say

- large count means datatypes that use MPI_Count to say how many
  elements they have:  a contig of 3 billion MPI_BYTES, say

Internally, though, there's no way to decouple those two problems.  

The changes are pervasive and make me really nervous.  

I've been sometimes pushing changes to the ticket-1742-bigio branch.

Who can review datatype changes once I'm done?:

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA