Subject: [PATCH RFC net-next 18/18] net/ipv4: Optimization for fib_info lookup

From: [email-masked]
Date: Fri, 31 Aug 2018 17:49:53 -0700

From: David Ahern <[email-masked]>

Be optimistic about re-using a fib_info when nexthop id is given and
the route does not use metrics. Avoids a memory allocation which in
most cases is expected to be freed anyways.

Signed-off-by: David Ahern <[email-masked]>
---
 net/ipv4/fib_semantics.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 0ddf14512bb3..e4411cd5514b 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -316,6 +316,19 @@ static inline unsigned int fib_devindex_hashfn(unsigned int val)
 		(val >> (DEVINDEX_HASHBITS * 2))) & mask;
 }
 
+static inline unsigned int fib_info_hashfn_cfg(const struct fib_config *cfg)
+{
+	unsigned int mask = (fib_info_hash_size - 1);
+	unsigned int val = 0;
+
+	val ^= (cfg->fc_protocol << 8) | cfg->fc_scope;
+	val ^= (__force u32)cfg->fc_prefsrc;
+	val ^= cfg->fc_priority;
+	val ^= fib_devindex_hashfn(cfg->fc_nh_id);
+
+	return (val ^ (val >> 7) ^ (val >> 12)) & mask;
+}
+
 static inline unsigned int fib_info_hashfn(const struct fib_info *fi)
 {
 	unsigned int mask = (fib_info_hash_size - 1);
@@ -334,6 +347,35 @@ static inline unsigned int fib_info_hashfn(const struct fib_info *fi)
 	return (val ^ (val >> 7) ^ (val >> 12)) & mask;
 }
 
+/* no metrics, only nexthop id */
+static struct fib_info *fib_find_info_nh(struct net *net,
+					 const struct fib_config *cfg)
+{
+	struct hlist_head *head;
+	struct fib_info *fi;
+	unsigned int hash;
+
+	hash = fib_info_hashfn_cfg(cfg);
+	head = &fib_info_hash[hash];
+
+	hlist_for_each_entry(fi, head, fib_hash) {
+		if (!net_eq(fi->fib_net, net))
+			continue;
+		if (!fi->nh || fi->nh->id != cfg->fc_nh_id)
+			continue;
+		if (cfg->fc_protocol == fi->fib_protocol &&
+		    cfg->fc_scope == fi->fib_scope &&
+		    cfg->fc_prefsrc == fi->fib_prefsrc &&
+		    cfg->fc_priority == fi->fib_priority &&
+		    cfg->fc_type == fi->fib_type &&
+		    cfg->fc_table == fi->fib_tb_id &&
+		    !((cfg->fc_flags ^ fi->fib_flags) & ~RTNH_COMPARE_MASK))
+			return fi;
+	}
+
+	return NULL;
+}
+
 static struct fib_info *fib_find_info(const struct fib_info *nfi)
 {
 	struct hlist_head *head;
@@ -1154,6 +1196,12 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 			goto err_inval;
 		}
 
+		if (!cfg->fc_mx) {
+			fi = fib_find_info_nh(net, cfg);
+			if (fi)
+				return fi;
+		}
+
 		nh = nexthop_find_by_id(net, cfg->fc_nh_id);
 		if (!nh) {
 			NL_SET_ERR_MSG(extack,
-- 
2.11.0