Commit f05a4819 authored by Alexander Duyck's avatar Alexander Duyck Committed by David S. Miller

fib_trie: Add functions should_inflate and should_halve

This change pulls the logic for if we should inflate/halve the nodes out
into separate functions.  It also addresses what I believe is a bug where 1
full node is all that is needed to keep a node from ever being halved.

Simple script to reproduce the issue:
	modprobe dummy;	ifconfig dummy0 up
	for i in `seq 0 255`; do ifconfig dummy0:$i 10.0.${i}.1/24 up; done
	ifconfig dummy0:256 10.0.255.33/16 up
	for i in `seq 0 254`; do ifconfig dummy0:$i down; done

Results from /proc/net/fib_triestat
Before:
	Local:
		Aver depth:     3.00
		Max depth:      4
		Leaves:         17
		Prefixes:       18
		Internal nodes: 11
		  1: 8  2: 2  10: 1
		Pointers: 1048
	Null ptrs: 1021
	Total size: 11  kB
After:
	Local:
		Aver depth:     3.41
		Max depth:      5
		Leaves:         17
		Prefixes:       18
		Internal nodes: 12
		  1: 8  2: 3  3: 1
		Pointers: 36
	Null ptrs: 8
	Total size: 3  kB
Signed-off-by: default avatarAlexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cf3637bb
...@@ -647,12 +647,94 @@ static struct tnode *halve(struct trie *t, struct tnode *oldtnode) ...@@ -647,12 +647,94 @@ static struct tnode *halve(struct trie *t, struct tnode *oldtnode)
return ERR_PTR(-ENOMEM); return ERR_PTR(-ENOMEM);
} }
/* From "Implementing a dynamic compressed trie" by Stefan Nilsson of
* the Helsinki University of Technology and Matti Tikkanen of Nokia
* Telecommunications, page 6:
* "A node is doubled if the ratio of non-empty children to all
* children in the *doubled* node is at least 'high'."
*
* 'high' in this instance is the variable 'inflate_threshold'. It
* is expressed as a percentage, so we multiply it with
* tnode_child_length() and instead of multiplying by 2 (since the
* child array will be doubled by inflate()) and multiplying
* the left-hand side by 100 (to handle the percentage thing) we
* multiply the left-hand side by 50.
*
* The left-hand side may look a bit weird: tnode_child_length(tn)
* - tn->empty_children is of course the number of non-null children
* in the current node. tn->full_children is the number of "full"
* children, that is non-null tnodes with a skip value of 0.
* All of those will be doubled in the resulting inflated tnode, so
* we just count them one extra time here.
*
* A clearer way to write this would be:
*
* to_be_doubled = tn->full_children;
* not_to_be_doubled = tnode_child_length(tn) - tn->empty_children -
* tn->full_children;
*
* new_child_length = tnode_child_length(tn) * 2;
*
* new_fill_factor = 100 * (not_to_be_doubled + 2*to_be_doubled) /
* new_child_length;
* if (new_fill_factor >= inflate_threshold)
*
* ...and so on, tho it would mess up the while () loop.
*
* anyway,
* 100 * (not_to_be_doubled + 2*to_be_doubled) / new_child_length >=
* inflate_threshold
*
* avoid a division:
* 100 * (not_to_be_doubled + 2*to_be_doubled) >=
* inflate_threshold * new_child_length
*
* expand not_to_be_doubled and to_be_doubled, and shorten:
* 100 * (tnode_child_length(tn) - tn->empty_children +
* tn->full_children) >= inflate_threshold * new_child_length
*
* expand new_child_length:
* 100 * (tnode_child_length(tn) - tn->empty_children +
* tn->full_children) >=
* inflate_threshold * tnode_child_length(tn) * 2
*
* shorten again:
* 50 * (tn->full_children + tnode_child_length(tn) -
* tn->empty_children) >= inflate_threshold *
* tnode_child_length(tn)
*
*/
static bool should_inflate(const struct tnode *tn)
{
unsigned long used = tnode_child_length(tn);
unsigned long threshold = used;
/* Keep root node larger */
threshold *= node_parent(tn) ? inflate_threshold :
inflate_threshold_root;
used += tn->full_children;
used -= tn->empty_children;
return tn->pos && ((50 * used) >= threshold);
}
static bool should_halve(const struct tnode *tn)
{
unsigned long used = tnode_child_length(tn);
unsigned long threshold = used;
/* Keep root node larger */
threshold *= node_parent(tn) ? halve_threshold :
halve_threshold_root;
used -= tn->empty_children;
return (tn->bits > 1) && ((100 * used) < threshold);
}
#define MAX_WORK 10 #define MAX_WORK 10
static struct tnode *resize(struct trie *t, struct tnode *tn) static struct tnode *resize(struct trie *t, struct tnode *tn)
{ {
struct tnode *old_tn, *n = NULL; struct tnode *old_tn, *n = NULL;
int inflate_threshold_use;
int halve_threshold_use;
int max_work; int max_work;
if (!tn) if (!tn)
...@@ -668,86 +750,12 @@ static struct tnode *resize(struct trie *t, struct tnode *tn) ...@@ -668,86 +750,12 @@ static struct tnode *resize(struct trie *t, struct tnode *tn)
/* One child */ /* One child */
if (tn->empty_children == (tnode_child_length(tn) - 1)) if (tn->empty_children == (tnode_child_length(tn) - 1))
goto one_child; goto one_child;
/*
* Double as long as the resulting node has a number of
* nonempty nodes that are above the threshold.
*/
/* /* Double as long as the resulting node has a number of
* From "Implementing a dynamic compressed trie" by Stefan Nilsson of * nonempty nodes that are above the threshold.
* the Helsinki University of Technology and Matti Tikkanen of Nokia
* Telecommunications, page 6:
* "A node is doubled if the ratio of non-empty children to all
* children in the *doubled* node is at least 'high'."
*
* 'high' in this instance is the variable 'inflate_threshold'. It
* is expressed as a percentage, so we multiply it with
* tnode_child_length() and instead of multiplying by 2 (since the
* child array will be doubled by inflate()) and multiplying
* the left-hand side by 100 (to handle the percentage thing) we
* multiply the left-hand side by 50.
*
* The left-hand side may look a bit weird: tnode_child_length(tn)
* - tn->empty_children is of course the number of non-null children
* in the current node. tn->full_children is the number of "full"
* children, that is non-null tnodes with a skip value of 0.
* All of those will be doubled in the resulting inflated tnode, so
* we just count them one extra time here.
*
* A clearer way to write this would be:
*
* to_be_doubled = tn->full_children;
* not_to_be_doubled = tnode_child_length(tn) - tn->empty_children -
* tn->full_children;
*
* new_child_length = tnode_child_length(tn) * 2;
*
* new_fill_factor = 100 * (not_to_be_doubled + 2*to_be_doubled) /
* new_child_length;
* if (new_fill_factor >= inflate_threshold)
*
* ...and so on, tho it would mess up the while () loop.
*
* anyway,
* 100 * (not_to_be_doubled + 2*to_be_doubled) / new_child_length >=
* inflate_threshold
*
* avoid a division:
* 100 * (not_to_be_doubled + 2*to_be_doubled) >=
* inflate_threshold * new_child_length
*
* expand not_to_be_doubled and to_be_doubled, and shorten:
* 100 * (tnode_child_length(tn) - tn->empty_children +
* tn->full_children) >= inflate_threshold * new_child_length
*
* expand new_child_length:
* 100 * (tnode_child_length(tn) - tn->empty_children +
* tn->full_children) >=
* inflate_threshold * tnode_child_length(tn) * 2
*
* shorten again:
* 50 * (tn->full_children + tnode_child_length(tn) -
* tn->empty_children) >= inflate_threshold *
* tnode_child_length(tn)
*
*/ */
/* Keep root node larger */
if (!node_parent(tn)) {
inflate_threshold_use = inflate_threshold_root;
halve_threshold_use = halve_threshold_root;
} else {
inflate_threshold_use = inflate_threshold;
halve_threshold_use = halve_threshold;
}
max_work = MAX_WORK; max_work = MAX_WORK;
while ((tn->full_children > 0 && max_work-- && while (should_inflate(tn) && max_work--) {
50 * (tn->full_children + tnode_child_length(tn)
- tn->empty_children)
>= inflate_threshold_use * tnode_child_length(tn))) {
old_tn = tn; old_tn = tn;
tn = inflate(t, tn); tn = inflate(t, tn);
...@@ -764,16 +772,11 @@ static struct tnode *resize(struct trie *t, struct tnode *tn) ...@@ -764,16 +772,11 @@ static struct tnode *resize(struct trie *t, struct tnode *tn)
if (max_work != MAX_WORK) if (max_work != MAX_WORK)
return tn; return tn;
/* /* Halve as long as the number of empty children in this
* Halve as long as the number of empty children in this
* node is above threshold. * node is above threshold.
*/ */
max_work = MAX_WORK; max_work = MAX_WORK;
while (tn->bits > 1 && max_work-- && while (should_halve(tn) && max_work--) {
100 * (tnode_child_length(tn) - tn->empty_children) <
halve_threshold_use * tnode_child_length(tn)) {
old_tn = tn; old_tn = tn;
tn = halve(t, tn); tn = halve(t, tn);
if (IS_ERR(tn)) { if (IS_ERR(tn)) {
......
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