netdev - Re: Massive hash collisions on FIB

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Message-ID: <CANn89iL5XEZ0S6c-amu_Q_k8fXYqDKLVh1bPv8kPhc4eKR6UYw@mail.gmail.com>
Date: Wed, 25 Sep 2024 22:12:06 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Alexandre Ferrieux <alexandre.ferrieux@...il.com>
Cc: Simon Horman <horms@...nel.org>, Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
	nicolas.dichtel@...nd.com, netdev@...r.kernel.org
Subject: Re: Massive hash collisions on FIB

On Wed, Sep 25, 2024 at 9:46 PM Alexandre Ferrieux
<alexandre.ferrieux@...il.com> wrote:
>
> On 25/09/2024 21:25, Eric Dumazet wrote:
> > On Wed, Sep 25, 2024 at 9:06 PM Alexandre Ferrieux
> >
> >> [...] why are
> >> the IPv4 and IPv6 FIB-exact-lookup implementations different/duplicated ?
> >
> > You know we make these kinds of changes whenever they are needed for
> > our workload.
> >
> > Just submit a patch, stop wondering why it was not already done.
>
> Sure, will do shortly.
>
> However, I was not wondering about the history behind net_hash_mix(), but more
> generally why there are two parallel implementations of FIB insertion.

ipv6 has been done after ipv4, and by different contributors.

BTW, inet6_addr_hash() does not really need the net_hash_mix() because ipv6 uses
a per-netns hashtable (net->ipv6.inet6_addr_lst[]), with pros and cons
(vs IPv4 resizable hashtable)