linux-kernel - Re: [PATCH v5 2/2] netfilter: save the hash of the tuple in the original direction for latter use

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Message-ID: <4C979515.4060908@trash.net>
Date:	Mon, 20 Sep 2010 19:08:37 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Changli Gao <xiaosuo@...il.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/2] netfilter: save the hash of the tuple in the original
 direction for latter use

On 20.09.2010 17:04, Changli Gao wrote:
> On Thu, Sep 16, 2010 at 2:18 PM, Patrick McHardy <kaber@...sh.net> wrote:
>> On 21.08.2010 00:49, Changli Gao wrote:
>>> Since we don't change the tuple in the original direction, we can save it
>>> in ct->tuplehash[IP_CT_DIR_REPLY].hnode.pprev for __nf_conntrack_confirm()
>>> use.
>>
>> I like this idea. We could actually do the same for the reply tuple
>> and invalidate the saved hash in case the reply tuple is changed
>> (nf_conntrack_alter_reply()), which only happens when NAT is used.
>>
> 
> We can't do that, as the unconfirmed ct owned maybe dropped, and
> pre-computing will wast CPU cycles in this case.

Sure we can, dropping unconfirmed conntracks is a rare exception,
not a common case. Even under DoS we usually drop *unassured*
conntracks, which have already enterered the hash. If we're unable
to do that, we won't even allocate a new conntrack.
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