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From: Alexander Duyck <alexander.h.duyck@redhat.com>
Date: Wed, 10 Dec 2014 21:49:22 -0800
Subject: [PATCH] fib_trie: Fix trie balancing issue if new node pushes down
existing node
This patch addresses an issue with the level compression of the fib_trie.
Specifically in the case of adding a new leaf that triggers a new node to
be added that takes the place of the old node. The result is a trie where
the 1 child tnode is on one side and one leaf is on the other which gives
you a very deep trie. Below is the script I used to generate a trie on
dummy0 with a 10.X.X.X family of addresses.
ip link add type dummy
ipval=184549374
bit=2
for i in `seq 1 23`
do
ifconfig dummy0:$bit $ipval/8
ipval=`expr $ipval - $bit`
bit=`expr $bit \* 2`
done
cat /proc/net/fib_triestat
Running the script before the patch:
Local:
Aver depth: 10.82
Max depth: 23
Leaves: 29
Prefixes: 30
Internal nodes: 27
1: 26 2: 1
Pointers: 56
Null ptrs: 1
Total size: 5 kB
After applying the patch and repeating:
Local:
Aver depth: 4.72
Max depth: 9
Leaves: 29
Prefixes: 30
Internal nodes: 12
1: 3 2: 2 3: 7
Pointers: 70
Null ptrs: 30
Total size: 4 kB
What this fix does is start the rebalance at the newly created tnode
instead of at the parent tnode. This way if there is a gap between the
parent and the new node it doesn't prevent the new tnode from being
coalesced with any pre-existing nodes that may have been pushed into one
of the new nodes child branches.
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
@@ -1143,8 +1143,9 @@ static struct list_head *fib_insert_node
put_child(tp, cindex, (struct rt_trie_node *)tn);
} else {
rcu_assign_pointer(t->trie, (struct rt_trie_node *)tn);
- tp = tn;
}
+
+ tp = tn;
}
if (tp && tp->pos + tp->bits > 32)
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