A garbage collector predicts future allocation requirements and then distributes free items to multiple subpool free lists and a TLH free list during the sweep phase according to the future allocation requirements. The sizes of subpools and number of free items in subpools are predicted as the most likely to match future allocation requests. Once a subpool free list is filled with the number of free items needed according to the future allocation requirements, any additional free items designated for the subpool free list can be divided into multiple TLH sized free items and placed on the TLH free list. Allocation threads are enabled to acquire free items from the TLH free list and to replenish a current TLH without acquiring heap lock.