A bitmask array is implemented as a two dimensional bit array where each bit represents an allocated/free cell of the heap. Groups of bits of the bitmask array are assigned to implement commonly sized memory cell allocation requests. The heap manager keeps track of allocations by keeping separate lists of which groups are being used to implement commonly sized memory cell allocations requests by maintaining linked lists according to the number of cells allocated per request. Each list contains a list of the bit groups that have been used to provide allocations for particularly sized requests. By maintaining lists based on allocation size, the heap manager is able to cause new allocation requests to be matched up with previously retired allocations of the same size. Memory may be dynamically allocated between lists of differently sized memory requests.