netdev - Re: [RFC 6/6] fib_trie: combine leaf and info

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Date:	Tue, 15 Jan 2008 19:32:31 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Stephen Hemminger <stephen.hemminger@...tta.com>
Cc:	Robert Olsson <Robert.Olsson@...a.slu.se>,
	David Miller <davem@...emloft.net>, robert.olsson@....uu.se,
	netdev@...r.kernel.org
Subject: Re: [RFC 6/6] fib_trie: combine leaf and info

On Tue, 15 Jan 2008 10:15:43 -0800
Stephen Hemminger <stephen.hemminger@...tta.com> wrote:

> On Tue, 15 Jan 2008 19:10:31 +0100
> Eric Dumazet <dada1@...mosbay.com> wrote:
> 
> > On Tue, 15 Jan 2008 09:47:53 -0800
> > Stephen Hemminger <stephen.hemminger@...tta.com> wrote:
> > 
> > > This is how I did it:
> > > 
> > > --- a/net/ipv4/fib_trie.c	2008-01-15 09:14:53.000000000 -0800
> > > +++ b/net/ipv4/fib_trie.c	2008-01-15 09:21:48.000000000 -0800
> > > @@ -101,13 +101,6 @@ struct node {
> > >  	t_key key;
> > >  };
> > >  
> > > -struct leaf {
> > > -	unsigned long parent;
> > > -	t_key key;
> > > -	struct hlist_head list;
> > > -	struct rcu_head rcu;
> > > -};
> > > -
> > >  struct leaf_info {
> > >  	struct hlist_node hlist;
> > >  	struct rcu_head rcu;
> > > @@ -115,6 +108,13 @@ struct leaf_info {
> > >  	struct list_head falh;
> > >  };
> > >  
> > > +struct leaf {
> > > +	unsigned long parent;
> > > +	t_key key;
> > > +	struct hlist_head list;
> > > +	struct rcu_head rcu;
> > > +};
> > 
> > I like this :)
> > 
> > Your design is clean, but we waste some space (rcu in leaf_info "included"), we probably can do a litle bit better
> > (moving rcu at the end of leaf_info, and kmem_cache_create("ip_fib_trie", sizeof(struct leaf) + sizeof(struct_leaf_info) - sizeof(struct rcu_head))
> > 
> >  
> > > -	trie_leaf_kmem = kmem_cache_create("ip_fib_trie", sizeof(struct leaf),
> > > +	trie_leaf_kmem = kmem_cache_create("ip_fib_trie",
> > > +					   sizeof(struct leaf) + sizeof(struct leaf_info),
> > >  					   0, SLAB_PANIC, NULL);
> > >  }
> > >  
> > > 
> > 
> > Thank you
> 
> Having multiple RCU links is a waste. I started on code that just splice's the
> leaf_info's off to a free_list and then do a mass free after and RCU barrier.
> 
> For the normal case of just freeing a leaf, it could just walk the chain
> in the RCU free of the leaf.

Well, If you take this path, we can also copy the leaf itself, and
just use a variable size array of infos[], no more list, and maximal locality

kmalloc(sizeof(leaf) + nb_infos * sizeof(info))

(Still we can use a kmem cache for nb_infos=1 leaves)

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