How to decide how much memory to allocate per core for MPI app GENE?

This is required information for some MPI using app that I am working with... From its Makefile *template*: #insert memory per core and uncomment the following line #PREPROC= -D'MB_PER_CORE=750' Note that said scientific app runs also on NUMA machines, like Cray, where each core has its own memory. I am asking here what to put in above line on ***Linux*** on e.g. 12GB machine with 16 cores.