Messages in this thread | | | From | Yafang Shao <> | Date | Tue, 7 Aug 2018 09:40:42 +0800 | Subject | Re: [PATCH net-next] tcp: fix the calculation of sysctl_max_tw_buckets in tcp_sk_init() |
| |
On Tue, Aug 7, 2018 at 4:41 AM, David Miller <davem@davemloft.net> wrote: > From: Yafang Shao <laoar.shao@gmail.com> > Date: Mon, 6 Aug 2018 19:47:00 +0800 > >> tcp_hashinfo.ehash_mask is always an odd number, which is set in function >> alloc_large_system_hash(). See bellow, >> if (_hash_mask) >> *_hash_mask = (1 << log2qty) - 1; <<< always odd number >> >> Hence the local variable 'cnt' is a even number, as a result of that it is >> no difference to do the incrementation here. >> >> Maybe the compiler could also optimize it, but this code is a little ugly. >> >> Fix: fee83d09 ("ipv4: Namespaceify tcp_max_syn_backlog knob") > > The correct tag is "Fixes: "
OK
> >> @@ -2543,7 +2543,7 @@ static int __net_init tcp_sk_init(struct net *net) >> net->ipv4.sysctl_tcp_tw_reuse = 2; >> >> cnt = tcp_hashinfo.ehash_mask + 1; >> - net->ipv4.tcp_death_row.sysctl_max_tw_buckets = (cnt + 1) / 2; >> + net->ipv4.tcp_death_row.sysctl_max_tw_buckets = cnt / 2; >> net->ipv4.tcp_death_row.hashinfo = &tcp_hashinfo; > > This is completely harmless, and does no harm. >
It is harmless, meanwhile, it is useless and a little ugly.
By the way, why do we init sysctl_max_tw_buckets to (tcp_hashinfo.ehash_mask + 1) / 2 or (tcp_hashinfo.ehash_mask + 2) / 2 ? Per my pespective, this default value is a little huge, sometimes we have to set this value to a lower value with sysctl, otherwise it may easily cause tcp port exhaustion issue. So why not just init it to a lower value ?
> You aren't "fixing" anything.
| |