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From: Alexander Duyck <alexander.h.duyck@redhat.com>
Date: Wed, 31 Dec 2014 10:56:37 -0800
Subject: [PATCH] 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: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -647,12 +647,94 @@ nomem:
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
static struct tnode *resize(struct trie *t, struct tnode *tn)
{
struct tnode *old_tn, *n = NULL;
- int inflate_threshold_use;
- int halve_threshold_use;
int max_work;
if (!tn)
@@ -668,86 +750,12 @@ static struct tnode *resize(struct trie
/* One child */
if (tn->empty_children == (tnode_child_length(tn) - 1))
goto one_child;
- /*
- * Double as long as the resulting node has a number of
- * nonempty nodes that are above the threshold.
- */
- /*
- * 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)
- *
+ /* Double as long as the resulting node has a number of
+ * nonempty nodes that are above the threshold.
*/
-
- /* 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;
- while ((tn->full_children > 0 && max_work-- &&
- 50 * (tn->full_children + tnode_child_length(tn)
- - tn->empty_children)
- >= inflate_threshold_use * tnode_child_length(tn))) {
-
+ while (should_inflate(tn) && max_work--) {
old_tn = tn;
tn = inflate(t, tn);
@@ -764,16 +772,11 @@ static struct tnode *resize(struct trie
if (max_work != MAX_WORK)
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.
*/
-
max_work = MAX_WORK;
- while (tn->bits > 1 && max_work-- &&
- 100 * (tnode_child_length(tn) - tn->empty_children) <
- halve_threshold_use * tnode_child_length(tn)) {
-
+ while (should_halve(tn) && max_work--) {
old_tn = tn;
tn = halve(t, tn);
if (IS_ERR(tn)) {
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