On Tue, Dec 15, 2020 at 5:55 PM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote: > > 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. Do you have any numbers to prove that max_entries > 1024 with n_buckets == 1024 would still provide the same level of performance?
