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

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Date:   Fri, 1 Dec 2017 09:47:42 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     netdev <netdev@...r.kernel.org>,
        "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 Fri, Dec 01, 2017 at 09:26:46AM -0800, Eric Dumazet wrote:
> 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 ;) )
Oops. Indeed. Thanks for pointing it out.