Memory Considerations

In all, the size of the shared-memory area devoted to point-to-point messages is

n * ( n - 1
)
  * (
      MPI_SHM_NUMPOSTBOX *
( 64 + MPI_SHM_SHORTMSGSIZE )
    + MPI_SHM_CPOOLSIZE
    )

bytes when per-connection pools are used (that is, when MPI_SHM_SBPOOLSIZE is not set) and

n * ( n - 1
) * MPI_SHM_NUMPOSTBOX *
( 64 + MPI_SHM_SHORTMSGSIZE )
+
n * MPI_SHM_SBPOOLSIZE

bytes when per-sender pools are used (that is, when MPI_SHM_SBPOOLSIZE is set).

Cyclic message passing limits the size of shared memory that is needed to transfer even arbitrarily large messages.