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Subject: Re: [OMPI devel] RFC: Changing 32-bit build behavior/sizes for MPI_Count and MPI_Offset
From: Dave Goodell (dgoodell) (dgoodell_at_[hidden])
Date: 2014-02-11 10:22:35


On Feb 10, 2014, at 6:14 PM, Jeff Squyres (jsquyres) <jsquyres_at_[hidden]> wrote:

> As a side effect, this means that -- for 32 bit builds -- we will not support large filesystems well (e.g., filesystems with 64 bit offsets). BlueGene is an example of such a system (not that OMPI supports BlueGene, but...).

To clarify and head off unnecessary quibbling, I'll point out that by "BlueGene", Jeff means "Blue Gene/P" (/Q is 64-bit). This issue applies to any machine with 32-bit addresses that might want to access files larger than 2 GiB.

> Specifically: for 32 bit builds, we'll only allow MPI_Offset to be 32 bits. I don't think that this is a major issue, because 32 bit builds are not a huge issue for the OMPI community, but I raise the point in the spirit of full disclosure. Fixing it to allow 32 bit MPI_Aint but 64 bit MPI_Offset and MPI_Count would likely mean re-tooling the PML/BML/BTL/convertor infrastructure to use something other than size_t, and I have zero desire to do that! (please, no OMPI vendor reveal that they're going to seriously build giant 32 bit systems...)

-Dave