From: Alexander Duyck 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 Signed-off-by: David S. Miller --- --- 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)) {