64KB bucket: Head -> [ A pool of 200 64KB "blocks", of which 50 are empty ] -> [ A pool of 100 64KB blocks, of which 30 are empty ] -> null 128KB bucket: Head -> [ A pool of 60 128KB "blocks", of which 25 are empty ] -> null 192KB bucket: Head -> null 256KB bucket: Head -> [ A pool of 40 256KB "blocks", of which 10 are empty ] -> [ A pool of 20 256KB blocks, of which 10 are emtpy ] -> [ A pool of 4 256 KB blocks of which 0 are empty ] -> null ... 4MB bucket: Head -> [ A pool of 2 4MB "blocks", of which 1 is empty ] -> null