From e962f30297491fddc55a432d5d37df33c83e06f2 Mon Sep 17 00:00:00 2001 From: Alexander Duyck 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 Signed-off-by: David S. Miller --- net/ipv4/fib_trie.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index e9cb2588e416..18bcaf2ff2fd 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -1143,8 +1143,9 @@ static struct list_head *fib_insert_node(struct trie *t, u32 key, int plen) 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) -- 2.20.1