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Date: Fri, 12 Dec 2014 10:54:25 -0500 (EST)
From: David Miller <davem@...emloft.net>
To: alexander.h.duyck@...hat.com
Cc: netdev@...r.kernel.org
Subject: Re: [net PATCH] fib_trie: Fix trie balancing issue if new node
pushes down existing node
From: David Miller <davem@...emloft.net>
Date: Thu, 11 Dec 2014 21:32:16 -0500 (EST)
> From: Alexander Duyck <alexander.h.duyck@...hat.com>
> Date: Wed, 10 Dec 2014 21:49:22 -0800
>
>> This patch addresses an issue with the level compression of the fib_trie.
>> Specifically in the case of adding a new leaf that triggers a new node to
>> be added that takes the place of the old node. The result is a trie where
>> the 1 child tnode is on one side and one leaf is on the other which gives
>> you a very deep trie. Below is the script I used to generate a trie on
>> dummy0 with a 10.X.X.X family of addresses.
> ...
>> What this fix does is start the rebalance at the newly created tnode
>> instead of at the parent tnode. This way if there is a gap between the
>> parent and the new node it doesn't prevent the new tnode from being
>> coalesced with any pre-existing nodes that may have been pushed into one
>> of the new nodes child branches.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...hat.com>
>
> One has to be mindful with this code that what it's doing now might
> be intentional. For example, it might be doing things this way
> on purpose in order to minimize rebalancing during route flaps.
>
> Barring anything like that, I think your change is fine.
Alex, in case it isn't clear, I'm hoping that you might have some
thoughts on this aspect of your changes. :)
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