searchlight: MPI does not fit in 'int' error #510

From Gitter:

Hello, I'm running a Brainiak searchlight (sl_rad = 3, max_blk_edge = 10, pool_size = 1) and getting errors from mpi4py (trace below). The searchlight loads 253GB of data. I'm using 3 Tiger cluster nodes (120 ranks in total) and the job uses 840GB of memory across all 3 nodes. The log shows an mpi4py error, a quick Google search suggests that this error crops up when the size of the pickled object is >2GB (https://githubmemory.com/repo/mpi4py/mpi4py/issues/119). Any suggestions for solving this issue would be much appreciated!

Traceback (most recent call last):
File "../notebooks/batch/delta_searchlight.py", line 899, in
main()
File "../notebooks/batch/delta_searchlight.py", line 880, in main
sl.distribute(full_set, sl_mask)
File "../.conda/envs/brainiak11/lib/python3.7/site-packages/brainiak/searchlight/searchlight.py", line 370, in distribute
for (s_idx, s) in enumerate(splitsubj)]
File "../.conda/envs/brainiak11/lib/python3.7/site-packages/brainiak/searchlight/searchlight.py", line 370, in
for (s_idx, s) in enumerate(splitsubj)]
File "../.conda/envs/brainiak11/lib/python3.7/site-packages/brainiak/searchlight/searchlight.py", line 310, in _scatter_list
mytrans = self.comm.scatter(padded, root=owner)
File "mpi4py/MPI/Comm.pyx", line 1267, in mpi4py.MPI.Comm.scatter
File "mpi4py/MPI/msgpickle.pxi", line 730, in mpi4py.MPI.PyMPI_scatter
File "mpi4py/MPI/msgpickle.pxi", line 125, in mpi4py.MPI.Pickle.dumpv
File "mpi4py/MPI/msgbuffer.pxi", line 44, in mpi4py.MPI.downcast
OverflowError: integer 2157576948 does not fit in 'int'