netdev - [PATCH][next-next][v2] netlink: avoid to allocate full skb when sending to many devices

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Message-Id: <1537433690-24335-1-git-send-email-lirongqing@baidu.com>
Date:   Thu, 20 Sep 2018 16:54:50 +0800
From:   Li RongQing <lirongqing@...du.com>
To:     netdev@...r.kernel.org
Subject: [PATCH][next-next][v2] netlink: avoid to allocate full skb when sending to many devices

if skb->head is vmalloc address, when this skb is delivered, full
allocation for this skb is required, if there are many devices,
the full allocation will be called for every devices

now if it is vmalloc, allocate a new skb, whose data is not vmalloc
address, and use new allocated skb to clone and send, to avoid to
allocate full skb everytime.

Signed-off-by: Zhang Yu <zhangyu31@...du.com>
Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 net/netlink/af_netlink.c | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index e3a0538ec0be..a5b1bf706526 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -279,21 +279,25 @@ static bool netlink_filter_tap(const struct sk_buff *skb)
 }
 
 static int __netlink_deliver_tap_skb(struct sk_buff *skb,
-				     struct net_device *dev)
+				 struct net_device *dev, bool alloc, bool last)
 {
 	struct sk_buff *nskb;
 	struct sock *sk = skb->sk;
 	int ret = -ENOMEM;
 
-	if (!net_eq(dev_net(dev), sock_net(sk)))
+	if (!net_eq(dev_net(dev), sock_net(sk))) {
+		if (last && alloc)
+			consume_skb(skb);
 		return 0;
+	}
 
 	dev_hold(dev);
 
-	if (is_vmalloc_addr(skb->head))
-		nskb = netlink_to_full_skb(skb, GFP_ATOMIC);
+	if (unlikely(last && alloc))
+		nskb = skb;
 	else
 		nskb = skb_clone(skb, GFP_ATOMIC);
+
 	if (nskb) {
 		nskb->dev = dev;
 		nskb->protocol = htons((u16) sk->sk_protocol);
@@ -303,6 +307,8 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb,
 		ret = dev_queue_xmit(nskb);
 		if (unlikely(ret > 0))
 			ret = net_xmit_errno(ret);
+	} else if (alloc) {
+		kfree_skb(skb);
 	}
 
 	dev_put(dev);
@@ -311,16 +317,33 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb,
 
 static void __netlink_deliver_tap(struct sk_buff *skb, struct netlink_tap_net *nn)
 {
+	struct netlink_tap *tmp, *next;
+	bool alloc = false;
 	int ret;
-	struct netlink_tap *tmp;
 
 	if (!netlink_filter_tap(skb))
 		return;
 
-	list_for_each_entry_rcu(tmp, &nn->netlink_tap_all, list) {
-		ret = __netlink_deliver_tap_skb(skb, tmp->dev);
+	tmp = list_first_or_null_rcu(&nn->netlink_tap_all,
+					struct netlink_tap, list);
+	if (!tmp)
+		return;
+
+	if (is_vmalloc_addr(skb->head)) {
+		skb = netlink_to_full_skb(skb, GFP_ATOMIC);
+		if (!skb)
+			return;
+		alloc = true;
+	}
+
+	while (tmp) {
+		next = list_next_or_null_rcu(&nn->netlink_tap_all, &tmp->list,
+					struct netlink_tap, list);
+
+		ret = __netlink_deliver_tap_skb(skb, tmp->dev, alloc, !next);
 		if (unlikely(ret))
 			break;
+		tmp = next;
 	}
 }
 
-- 
2.16.2