netdev - Re: [PATCH net-next 3/4] inet: Add a 2nd listener hashtable (port+addr)

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Date:   Fri, 01 Dec 2017 09:26:46 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Martin KaFai Lau <kafai@...com>, netdev <netdev@...r.kernel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net-next 3/4] inet: Add a 2nd listener hashtable
 (port+addr)

On Thu, 2017-11-30 at 15:23 -0800, Martin KaFai Lau wrote:
> The current listener hashtable is hashed by port only.
> When a process is listening at many IP addresses with the same port
> (e.g.
> [IP1]:443, [IP2]:443... [IPN]:443), the inet[6]_lookup_listener()
> performance is degraded to a link list.  It is prone to syn attack.
> 
> 

...

> diff --git a/include/net/inet_hashtables.h
> b/include/net/inet_hashtables.h
> index 4cce516c41ac..ebce55d694e7 100644
> --- a/include/net/inet_hashtables.h
> +++ b/include/net/inet_hashtables.h
> @@ -152,8 +152,19 @@ struct inet_hashinfo {
>  	 */
>  	struct inet_listen_hashbucket	listening_hash[INET_LHT
> ABLE_SIZE]
>  					____cacheline_aligned_in_smp
> ;
> +	struct inet_listen_hashbucket	*lhash2;
> +	unsigned int			lhash2_mask;
>  };
> 

Please move these two fields before listening_hash[], to avoid adding
another cache line to "struct inet_hashinfo"

( We have a 16-byte hole there, so lets use it ;) )