following the requests from Xavier and Jesse I introduced a
configuration parameter for the maximum memory per NUMA node. The
DIG_BANKSHIFT is set accordingly, the current choices are:
         512MB/bank:  16GB/node,
        2048MB/bank:  64GB/node,
        8192MB/bank: 256GB/node.

The patch is for 2.5.50+ia64. Please consider applying it.