netdev - Re: [PATCH v2 net 2/2] ipv4: add net_hash_mix() dispersion to fib_info

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Date:   Wed, 19 Jan 2022 08:40:54 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     David Ahern <dsahern@...nel.org>, netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 net 2/2] ipv4: add net_hash_mix() dispersion to
 fib_info_laddrhash keys

On 1/19/22 3:04 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> net/ipv4/fib_semantics.c uses a hash table (fib_info_laddrhash)
> in which fib_sync_down_addr() can locate fib_info
> based on IPv4 local address.
> 
> This hash table is resized based on total number of
> hashed fib_info, but the hash function is only
> using the local address.
> 
> For hosts having many active network namespaces,
> all fib_info for loopback devices (IPv4 address 127.0.0.1)
> are hashed into a single bucket, making netns dismantles
> very slow.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv4/fib_semantics.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@...nel.org>