request memory from kernel

HI I would like to reserve some of the system memory for our kernel modules. After some googling there seems to be there are different ways of doing this but still I am not clear. My question is if I want to put aside some portion of the our platform memory (about 300 Mbytes) for couple of our kernel modules, how could I achieve this and how to access the dedicated memory for those modules at the run time. Many thanks in advance, B