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>
This commit is contained in:
Alexander Duyck
David S. Miller
Родитель
cf3637bb8f
Коммит
f05a48198b
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@ -647,12 +647,94 @@ nomem:
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return ERR_PTR(-ENOMEM);
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}
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/* From "Implementing a dynamic compressed trie" by Stefan Nilsson of
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* the Helsinki University of Technology and Matti Tikkanen of Nokia
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* Telecommunications, page 6:
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* "A node is doubled if the ratio of non-empty children to all
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* children in the *doubled* node is at least 'high'."
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*
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* 'high' in this instance is the variable 'inflate_threshold'. It
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* is expressed as a percentage, so we multiply it with
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* tnode_child_length() and instead of multiplying by 2 (since the
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* child array will be doubled by inflate()) and multiplying
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* the left-hand side by 100 (to handle the percentage thing) we
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* multiply the left-hand side by 50.
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*
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* The left-hand side may look a bit weird: tnode_child_length(tn)
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* - tn->empty_children is of course the number of non-null children
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* in the current node. tn->full_children is the number of "full"
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* children, that is non-null tnodes with a skip value of 0.
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* All of those will be doubled in the resulting inflated tnode, so
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* we just count them one extra time here.
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*
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* A clearer way to write this would be:
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*
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* to_be_doubled = tn->full_children;
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* not_to_be_doubled = tnode_child_length(tn) - tn->empty_children -
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* tn->full_children;
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*
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* new_child_length = tnode_child_length(tn) * 2;
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*
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* new_fill_factor = 100 * (not_to_be_doubled + 2*to_be_doubled) /
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* new_child_length;
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* if (new_fill_factor >= inflate_threshold)
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*
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* ...and so on, tho it would mess up the while () loop.
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*
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* anyway,
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* 100 * (not_to_be_doubled + 2*to_be_doubled) / new_child_length >=
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* inflate_threshold
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*
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* avoid a division:
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* 100 * (not_to_be_doubled + 2*to_be_doubled) >=
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* inflate_threshold * new_child_length
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*
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* expand not_to_be_doubled and to_be_doubled, and shorten:
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* 100 * (tnode_child_length(tn) - tn->empty_children +
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* tn->full_children) >= inflate_threshold * new_child_length
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*
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* expand new_child_length:
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* 100 * (tnode_child_length(tn) - tn->empty_children +
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* tn->full_children) >=
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* inflate_threshold * tnode_child_length(tn) * 2
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*
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* shorten again:
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* 50 * (tn->full_children + tnode_child_length(tn) -
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* tn->empty_children) >= inflate_threshold *
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* tnode_child_length(tn)
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*
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*/
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static bool should_inflate(const struct tnode *tn)
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{
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unsigned long used = tnode_child_length(tn);
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unsigned long threshold = used;
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/* Keep root node larger */
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threshold *= node_parent(tn) ? inflate_threshold :
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inflate_threshold_root;
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used += tn->full_children;
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used -= tn->empty_children;
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return tn->pos && ((50 * used) >= threshold);
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}
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static bool should_halve(const struct tnode *tn)
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{
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unsigned long used = tnode_child_length(tn);
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unsigned long threshold = used;
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/* Keep root node larger */
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threshold *= node_parent(tn) ? halve_threshold :
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halve_threshold_root;
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used -= tn->empty_children;
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return (tn->bits > 1) && ((100 * used) < threshold);
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}
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#define MAX_WORK 10
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static struct tnode *resize(struct trie *t, struct tnode *tn)
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{
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struct tnode *old_tn, *n = NULL;
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int inflate_threshold_use;
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int halve_threshold_use;
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int max_work;
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if (!tn)
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@ -668,86 +750,12 @@ static struct tnode *resize(struct trie *t, struct tnode *tn)
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/* One child */
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if (tn->empty_children == (tnode_child_length(tn) - 1))
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goto one_child;
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/*
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* Double as long as the resulting node has a number of
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/* Double as long as the resulting node has a number of
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* nonempty nodes that are above the threshold.
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*/
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/*
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* From "Implementing a dynamic compressed trie" by Stefan Nilsson of
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* the Helsinki University of Technology and Matti Tikkanen of Nokia
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* Telecommunications, page 6:
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* "A node is doubled if the ratio of non-empty children to all
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* children in the *doubled* node is at least 'high'."
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*
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* 'high' in this instance is the variable 'inflate_threshold'. It
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* is expressed as a percentage, so we multiply it with
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* tnode_child_length() and instead of multiplying by 2 (since the
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* child array will be doubled by inflate()) and multiplying
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* the left-hand side by 100 (to handle the percentage thing) we
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* multiply the left-hand side by 50.
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*
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* The left-hand side may look a bit weird: tnode_child_length(tn)
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* - tn->empty_children is of course the number of non-null children
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* in the current node. tn->full_children is the number of "full"
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* children, that is non-null tnodes with a skip value of 0.
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* All of those will be doubled in the resulting inflated tnode, so
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* we just count them one extra time here.
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*
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* A clearer way to write this would be:
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*
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* to_be_doubled = tn->full_children;
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* not_to_be_doubled = tnode_child_length(tn) - tn->empty_children -
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* tn->full_children;
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*
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* new_child_length = tnode_child_length(tn) * 2;
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*
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* new_fill_factor = 100 * (not_to_be_doubled + 2*to_be_doubled) /
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* new_child_length;
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* if (new_fill_factor >= inflate_threshold)
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*
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* ...and so on, tho it would mess up the while () loop.
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*
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* anyway,
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* 100 * (not_to_be_doubled + 2*to_be_doubled) / new_child_length >=
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* inflate_threshold
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*
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* avoid a division:
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* 100 * (not_to_be_doubled + 2*to_be_doubled) >=
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* inflate_threshold * new_child_length
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*
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* expand not_to_be_doubled and to_be_doubled, and shorten:
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* 100 * (tnode_child_length(tn) - tn->empty_children +
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* tn->full_children) >= inflate_threshold * new_child_length
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*
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* expand new_child_length:
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* 100 * (tnode_child_length(tn) - tn->empty_children +
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* tn->full_children) >=
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* inflate_threshold * tnode_child_length(tn) * 2
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*
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* shorten again:
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* 50 * (tn->full_children + tnode_child_length(tn) -
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* tn->empty_children) >= inflate_threshold *
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* tnode_child_length(tn)
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*
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*/
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/* Keep root node larger */
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if (!node_parent(tn)) {
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inflate_threshold_use = inflate_threshold_root;
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halve_threshold_use = halve_threshold_root;
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} else {
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inflate_threshold_use = inflate_threshold;
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halve_threshold_use = halve_threshold;
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}
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max_work = MAX_WORK;
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while ((tn->full_children > 0 && max_work-- &&
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50 * (tn->full_children + tnode_child_length(tn)
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- tn->empty_children)
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>= inflate_threshold_use * tnode_child_length(tn))) {
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while (should_inflate(tn) && max_work--) {
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old_tn = tn;
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tn = inflate(t, tn);
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@ -764,16 +772,11 @@ static struct tnode *resize(struct trie *t, struct tnode *tn)
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if (max_work != MAX_WORK)
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return tn;
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/*
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* Halve as long as the number of empty children in this
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/* Halve as long as the number of empty children in this
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* node is above threshold.
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*/
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max_work = MAX_WORK;
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while (tn->bits > 1 && max_work-- &&
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100 * (tnode_child_length(tn) - tn->empty_children) <
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halve_threshold_use * tnode_child_length(tn)) {
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while (should_halve(tn) && max_work--) {
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old_tn = tn;
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tn = halve(t, tn);
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if (IS_ERR(tn)) {
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