netdev - Re: [PATCH net] ipv4: avoid quadratic behavior in FIB insertion of common address

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Message-ID: <CANn89iKDuODR=HasPhEkp6tFFD0-kcU2cZRgWenDr6fsPcziuA@mail.gmail.com>
Date: Thu, 26 Sep 2024 09:42:48 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Alexandre Ferrieux <alexandre.ferrieux@...il.com>
Cc: alexandre.ferrieux@...nge.com, nicolas.dichtel@...nd.com, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv4: avoid quadratic behavior in FIB insertion of
 common address

On Wed, Sep 25, 2024 at 11:29 PM Alexandre Ferrieux
<alexandre.ferrieux@...il.com> wrote:
>
> Mix netns into all IPv4 FIB hashes to avoid massive collision when
> inserting the same address in many netns.
>
> Signed-off-by: Alexandre Ferrieux <alexandre.ferrieux@...nge.com>

I think this targets net-next tree, which re-opens next week.


> ---
>  net/ipv4/fib_semantics.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index ba2df3d2ac15..89fa8fd1a4a5 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -347,10 +347,12 @@ static unsigned int fib_info_hashfn_1(int init_val, u8 protocol, u8 scope,
>         return val;
>  }
>
> -static unsigned int fib_info_hashfn_result(unsigned int val)
> +static unsigned int fib_info_hashfn_result(struct net *net, unsigned int val)

This can be 'const struct net *net'

>  {
>         unsigned int mask = (fib_info_hash_size - 1);

mask can be deleted, see below.

>
> +       val ^= net_hash_mix(net);
> +
>         return (val ^ (val >> 7) ^ (val >> 12)) & mask;

Please replace this legacy stuff with something more generic :

return hash_32(val ^ net_hash_mix(net), fib_info_hash_bits);

>  }
>
> @@ -370,7 +372,7 @@ static inline unsigned int fib_info_hashfn(struct fib_info *fi)
>                 } endfor_nexthops(fi)
>         }
>