netdev - Re: [PATCH net-next] netns: get more entropy from net_hash

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Message-Id: <20180623.110031.1772156487037263440.davem@davemloft.net>
Date:   Sat, 23 Jun 2018 11:00:31 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] netns: get more entropy from net_hash_mix()

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 22 Jun 2018 16:27:47 -0700

> struct net are effectively allocated from order-1 pages on x86,
> with one object per slab, meaning that the 13 low order bits
> of their addresses are zero.
> 
> Once shifted by L1_CACHE_SHIFT, this leaves 7 zero-bits,
> meaning that net_hash_mix() does not help spreading
> objects on various hash tables.
> 
> For example, TCP listen table has 32 buckets, meaning that
> all netns use the same bucket for port 80 or port 443.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Maciej Żenczykowski <maze@...gle.com>

Good catch, applied, thanks Eric.