[PATCH net 2/2] ipv4: add net_hash_mix() dispersion to fib_info_laddrhash keys

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

net/ipv4/fib_semantics.c uses a hash table (fib_info_laddrhash)
in which fib_sync_down_addr() can locate fib_info
based on IPv4 local address.

This hash table is resized based on total number of
hashed fib_info, but the hash function is only
using the local address.

For hosts having many active network namespaces,
all fib_info for loopback devices (IPv4 address 127.0.0.1)
are hashed into a single bucket, making netns dismantles
very slow.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/fib_semantics.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 9813949da10493de36b9db797b6a5d94fd9bd3b1..7971889fc0fe3690e47931c39e6a8f8e0fb1d31f 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -52,6 +52,7 @@ static DEFINE_SPINLOCK(fib_info_lock);
 static struct hlist_head *fib_info_hash;
 static struct hlist_head *fib_info_laddrhash;
 static unsigned int fib_info_hash_size;
+static unsigned int fib_info_hash_bits;
 static unsigned int fib_info_cnt;
 
 #define DEVINDEX_HASHBITS 8
@@ -1247,13 +1248,9 @@ int fib_check_nh(struct net *net, struct fib_nh *nh, u32 table, u8 scope,
 	return err;
 }
 
-static inline unsigned int fib_laddr_hashfn(__be32 val)
+static inline unsigned int fib_laddr_hashfn(const struct net *net, __be32 val)
 {
-	unsigned int mask = (fib_info_hash_size - 1);
-
-	return ((__force u32)val ^
-		((__force u32)val >> 7) ^
-		((__force u32)val >> 14)) & mask;
+	return hash_32(net_hash_mix(net) ^ (__force u32)val, fib_info_hash_bits);
 }
 
 static struct hlist_head *fib_info_hash_alloc(int bytes)
@@ -1289,6 +1286,7 @@ static void fib_info_hash_move(struct hlist_head *new_info_hash,
 	old_info_hash = fib_info_hash;
 	old_laddrhash = fib_info_laddrhash;
 	fib_info_hash_size = new_size;
+	fib_info_hash_bits = ilog2(new_size);
 
 	for (i = 0; i < old_size; i++) {
 		struct hlist_head *head = &fib_info_hash[i];
@@ -1315,7 +1313,7 @@ static void fib_info_hash_move(struct hlist_head *new_info_hash,
 			struct hlist_head *ldest;
 			unsigned int new_hash;
 
-			new_hash = fib_laddr_hashfn(fi->fib_prefsrc);
+			new_hash = fib_laddr_hashfn(fi->fib_net, fi->fib_prefsrc);
 			ldest = &new_laddrhash[new_hash];
 			hlist_add_head(&fi->fib_lhash, ldest);
 		}
@@ -1605,7 +1603,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 	if (fi->fib_prefsrc) {
 		struct hlist_head *head;
 
-		head = &fib_info_laddrhash[fib_laddr_hashfn(fi->fib_prefsrc)];
+		head = &fib_info_laddrhash[fib_laddr_hashfn(net, fi->fib_prefsrc)];
 		hlist_add_head(&fi->fib_lhash, head);
 	}
 	if (fi->nh) {
@@ -1877,16 +1875,16 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
  */
 int fib_sync_down_addr(struct net_device *dev, __be32 local)
 {
-	int ret = 0;
-	unsigned int hash = fib_laddr_hashfn(local);
-	struct hlist_head *head = &fib_info_laddrhash[hash];
 	int tb_id = l3mdev_fib_table(dev) ? : RT_TABLE_MAIN;
 	struct net *net = dev_net(dev);
+	struct hlist_head *head;
 	struct fib_info *fi;
+	int ret = 0;
 
 	if (!fib_info_laddrhash || local == 0)
 		return 0;
 
+	head = &fib_info_laddrhash[fib_laddr_hashfn(net, local)];
 	hlist_for_each_entry(fi, head, fib_lhash) {
 		if (!net_eq(fi->fib_net, net) ||
 		    fi->fib_tb_id != tb_id)
-- 
2.34.1.703.g22d0c6ccf7-goog