Even after clear, seems to be memory is not cleaned up when I use boost::fast_pool_allocator. Can someone help in correct usage? typedef std::set<unsigned int, std::less< unsigned int>, boost::fast_pool_allocator< unsigned int> > IDSET; int main() { IDSET set; WriteMemoryUsage(); for (int i=0;i<1000000;i++) set.insert(i); WriteMemoryUsage(); set.clear(); WriteMemoryUsage(); return 1; } In WriteMemoryUsage Processid: 4836 Peak Memory used: 1155072 Working Set Size: 2744320 Page File Usage: 1155072 Processid: 4836 Peak Memory used: 34816000 Working Set Size: 36528128 Page File Usage: 34816000 Processid: 4836 Peak Memory used: 34816000 Working Set Size: 36532224 Page File Usage: 34816000 Regards, UJ