Commit e6308be8 authored by Robert Olsson's avatar Robert Olsson Committed by David S. Miller
Browse files

[IPV4]: fib_trie root-node expansion 



The patch below introduces special thresholds to keep root node in the trie 
large. This gives a flatter tree at the cost of a modest memory increase.
Overall it seems to be gain and this was also proposed by one the authors 
of the paper in recent a seminar.

Main table after loading 123 k routes.

	Aver depth:     3.30
	Max depth:      9
        Root-node size  12 bits
        Total size: 4044  kB

With the patch:
	Aver depth:     2.78
	Max depth:      8
        Root-node size  15 bits
        Total size: 4150  kB

An increase of 8-10% was seen in forwading performance for an rDoS attack. 

Signed-off-by: default avatarRobert Olsson <robert.olsson@its.uu.se>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 87bf9c97

net/ipv4/fib_trie.c

+21 −2
Original line number Diff line number Diff line
@@ -286,6 +286,8 @@ static inline void check_tnode(const struct tnode *tn) 


static int halve_threshold = 25;

static int inflate_threshold = 50;

static int halve_threshold_root = 15;

static int inflate_threshold_root = 25; 





static void __alias_free_mem(struct rcu_head *head)
@@ -449,6 +451,8 @@ static struct node *resize(struct trie *t, struct tnode *tn) 
	int i;

	int err = 0;

	struct tnode *old_tn;

	int inflate_threshold_use;

	int halve_threshold_use;



 	if (!tn)

		return NULL;
@@ -541,10 +545,17 @@ static struct node *resize(struct trie *t, struct tnode *tn) 


	check_tnode(tn);



	/* Keep root node larger  */



	if(!tn->parent)

		inflate_threshold_use = inflate_threshold_root;

	else 

		inflate_threshold_use = inflate_threshold;



	err = 0;

	while ((tn->full_children > 0 &&

	       50 * (tn->full_children + tnode_child_length(tn) - tn->empty_children) >=

				inflate_threshold * tnode_child_length(tn))) {

				inflate_threshold_use * tnode_child_length(tn))) {



		old_tn = tn;

		tn = inflate(t, tn);
@@ -564,10 +575,18 @@ static struct node *resize(struct trie *t, struct tnode *tn) 
	 * node is above threshold.

	 */





	/* Keep root node larger  */



	if(!tn->parent)

		halve_threshold_use = halve_threshold_root;

	else 

		halve_threshold_use = halve_threshold;



	err = 0;

	while (tn->bits > 1 &&

	       100 * (tnode_child_length(tn) - tn->empty_children) <

	       halve_threshold * tnode_child_length(tn)) {

	       halve_threshold_use * tnode_child_length(tn)) {



		old_tn = tn;

		tn = halve(t, tn);

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