netdev - Re: [PATCH 1/3] inetpeer: Support ipv6 addresses.

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Date:	Tue, 30 Nov 2010 06:42:16 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	xiaosuo@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 1/3] inetpeer: Support ipv6 addresses.

Le lundi 29 novembre 2010 à 21:22 -0800, David Miller a écrit :
> From: Changli Gao <xiaosuo@...il.com>
> Date: Tue, 30 Nov 2010 12:51:08 +0800
> 
> > On Tue, Nov 30, 2010 at 11:14 AM, David Miller <davem@...emloft.net> wrote:
> >> From: Changli Gao <xiaosuo@...il.com>
> >> Date: Tue, 30 Nov 2010 10:33:49 +0800
> >>
> >>> I have thought about converting this AVL tree to rbtree. When I saw
> >>> the comment above, I gave it up, because rbtree makes this structure
> >>> bigger. If ipv6 support is added, I think it is time to turn to
> >>> rbtree. :)
> >>
> >> If it takes size over 128 bytes, it is probably still a bad idea.
> >> Right now it is just under 128.
> >>
> > 
> > Why 128? The current size of inet_peer is 64 bytes, and after your
> > ipv6 patch, it is just 80. And, inet_peer is allocated from its own
> > mem_cache, so the size of the memory for it should not be aligned to
> > 2^n.
> 
> Sorry, I was taking into the consideration other work I am doing
> which will move all of the routing metrics into inet_peer as well.
> 
> With ipv6 address support, it fits perfectly into 128 bytes on
> 64-bit.
> --

Its a bit early in the morning here, I must confess I dont yet
understand your patch David :)

As we use a tree, why not using two different trees for ipv4 / ipv6 ?

I dont understand how computing a 32bit key (sort of hash key) is going
to help when hash collision happens, with an avl tree.

For Changli : AVL tree was OK for RCU conversion, I am not sure about
RBtree yet.

Either version of tree (AVL/rbtree) will be expensive to use if depth is
big (With 2 millions entries, depth is going to be very big). I
understand you want to get rid of route cache ?

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