There is no need to memset released pages because they are already
zero. On db845c, before:
BM_stdlib_malloc_free_default/131072 34562 ns 34547 ns 20258 bytes_per_second=3.53345G/s
after:
BM_stdlib_malloc_free_default/131072 29618 ns 29589 ns 23485 bytes_per_second=4.12548G/s