On Tue, Dec 15, 2020 at 5:45 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Dec 15, 2020 at 1:44 PM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote: > > > > Hello, > > > > Any reason why we allocate at least max_entries of buckets of a hash map? > > > > 466 > > 467 /* hash table size must be power of 2 */ > > 468 htab->n_buckets = roundup_pow_of_two(htab->map.max_entries); > > because hashmap performance matters a lot. Unless you believe hash is perfect, there is always conflict no matter how many buckets we have. Other hashmap implementations also care about performance, but none of them allocates the number of buckets in this aggressive way. In some particular cases, for instance max_entries=1025, we end up having almost buckets twice of max_entries. Thanks.
