alloc_bitset
mq->hotspot_hit_bits = alloc_bitset(mq->nr_hotspot_blocks);
mq->cache_hit_bits = alloc_bitset(from_cblock(cache_size));
cache->dirty_bitset = alloc_bitset(from_cblock(cache->cache_size));
cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
cache->invalid_bitset = alloc_bitset(from_cblock(cache->cache_size));