netdev - Re: [PATCH net-next] ipv4: tcp: dont cache unconfirmed intput dst

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Message-Id: <20120627.170830.811332455348620174.davem@davemloft.net>
Date:	Wed, 27 Jun 2012 17:08:30 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, hans.schillstrom@...csson.com
Subject: Re: [PATCH net-next] ipv4: tcp: dont cache unconfirmed intput dst

From: David Miller <davem@...emloft.net>
Date: Wed, 27 Jun 2012 17:01:01 -0700 (PDT)

> There are quite a number of unwanted side effects from this change, so
> I think we'll have to revert unless you can fix up all of the relevant
> cases quickly.

Actually I've decided to revert it now.

Whilst this was a swell idea, there is no way for you to know if
we should really create a cached route or not.

Even if you could, there is a lot of logic you'll need to code up
so that, f.e., once we determine that we've got a DST_NOCACHE route
when we move to established state, we can insert it into the routing
cache and not mark it DST_NOCACHE any longer.

But even if we did that, we're going to eat 2 uncached route lookups
for every new incoming legitimate connection.
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