netdev - [PATCH net-next v2] ipv4: avoid quadratic behavior in FIB insertion of common address

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Message-Id: <20241001231438.3855035-1-alexandre.ferrieux@orange.com>
Date: Wed,  2 Oct 2024 01:14:38 +0200
From: Alexandre Ferrieux <alexandre.ferrieux@...il.com>
To: edumazet@...gle.com
Cc: alexandre.ferrieux@...nge.com,
	nicolas.dichtel@...nd.com,
	netdev@...r.kernel.org
Subject: [PATCH net-next v2] ipv4: avoid quadratic behavior in FIB insertion of common address

Mix netns into all IPv4 FIB hashes to avoid massive collision when
inserting the same address in many netns.

Signed-off-by: Alexandre Ferrieux <alexandre.ferrieux@...nge.com>
---
 net/ipv4/fib_semantics.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index ba2df3d2ac15..1a847ba40458 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -347,11 +347,10 @@ static unsigned int fib_info_hashfn_1(int init_val, u8 protocol, u8 scope,
 	return val;
 }
 
-static unsigned int fib_info_hashfn_result(unsigned int val)
+static unsigned int fib_info_hashfn_result(const struct net *net,
+					   unsigned int val)
 {
-	unsigned int mask = (fib_info_hash_size - 1);
-
-	return (val ^ (val >> 7) ^ (val >> 12)) & mask;
+	return hash_32(val ^ net_hash_mix(net), fib_info_hash_bits);
 }
 
 static inline unsigned int fib_info_hashfn(struct fib_info *fi)
@@ -370,7 +369,7 @@ static inline unsigned int fib_info_hashfn(struct fib_info *fi)
 		} endfor_nexthops(fi)
 	}
 
-	return fib_info_hashfn_result(val);
+	return fib_info_hashfn_result(fi->fib_net, val);
 }
 
 /* no metrics, only nexthop id */
@@ -385,7 +384,7 @@ static struct fib_info *fib_find_info_nh(struct net *net,
 				 cfg->fc_protocol, cfg->fc_scope,
 				 (__force u32)cfg->fc_prefsrc,
 				 cfg->fc_priority);
-	hash = fib_info_hashfn_result(hash);
+	hash = fib_info_hashfn_result(net, hash);
 	head = &fib_info_hash[hash];
 
 	hlist_for_each_entry(fi, head, fib_hash) {
-- 
2.30.2