netdev - Re: [RFC PATCH] netfilter: conntrack: cache route for forwarded connections

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Message-ID: <alpine.LFD.2.11.1412020827260.1593@ja.home.ssi.bg>
Date:	Tue, 2 Dec 2014 09:15:32 +0200 (EET)
From:	Julian Anastasov <ja@....bg>
To:	Florian Westphal <fw@...len.de>
cc:	netfilter-devel@...r.kernel.org, brouer@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] netfilter: conntrack: cache route for forwarded
 connections


	Hello,

On Tue, 2 Dec 2014, Florian Westphal wrote:

> ... to avoid per-packet FIB lookup if possible.
> 
> The cached dst is re-used provided the input interface
> is the same as that of the previous packet in the same direction.
> 
> If not, the cached dst is invalidated.
> 
> This should speed up forwarding when conntrack is already in use
> anyway, especially when using reverse path filtering -- active RPF
> enforces two FIB lookups for each packet.
> 
> Before the routing cache removal this didn't matter since RPF
> was performed only when route cache didn't yield a result; but without
> route cache it comes at high price.
> 
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
>  Sending as RFC since I haven't tested this yet (aside from
>  single-forwarded-flow), so no performance data either.
> 
>   - doesn't work when iif changes (it invalidates cached dst), don't
>   think its a problem

	The idea is good. But code that caches dsts should
also handle at least NETDEV_UNREGISTER (NETDEV_DOWN being
another option) to release dsts. Holding dsts for frozen
conns in EST state for long time is a problem. IIRC, such dsts
are not under dst_dev_event() control. nf_nat_masquerade_ipv4.c
has something like this but for masq_index.

Regards

--
Julian Anastasov <ja@....bg>
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