netdev - Re: [PATCH 0/5] Long term PMTU/redirect storage in ipv4.

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Date:	Tue, 17 Jul 2012 23:41:16 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	David Miller <davem@...emloft.net>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 0/5] Long term PMTU/redirect storage in ipv4.


	Hello,

On Tue, 17 Jul 2012, David Miller wrote:

> These patches implement the final mechanism necessary to really allow
> us to go without the route cache in ipv4.
> 
> We need a place to have long-term storage of PMTU/redirect information
> which is independent of the routes themselves, yet does not get us
> back into a situation where we have to write to metrics or anything
> like that.
> 
> For this we use an "next-hop exception" table in the FIB nexthops.
> 
> Currently it is a simple linked list and uses a single global lock
> for synchronization, but that can be easily adjusted as-needed.
> 
> The one thing I desperately want to avoid is having to create clone
> routes in the FIB trie for this purpose, because that is very
> expensive.   However, I'm willing to entertain such an idea later
> if this current scheme proves to have downsides that the FIB trie
> variant would not have.

	IIRC, struct fib_info was shared by different
prefixes. It saves a lot of memory when thousands of
routes are created to same GW. Now if we end up with 1 or
2 fib_info structures for default routes, the nh_exceptions list
can become very long. May be fib_info is not a good place
to hide such data.

Regards

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