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

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Date:   Thu, 20 Sep 2018 06:51:47 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Li RongQing <lirongqing@...du.com>, netdev@...r.kernel.org
Subject: Re: [PATCH][next-next][v2] netlink: avoid to allocate full skb when
 sending to many devices



On 09/20/2018 06:43 AM, Eric Dumazet wrote:
> 

> And lastly this patch looks way too complicated to me.
> You probably can write something much simpler.

Something like :

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 930d17fa906c9ebf1cf7b6031ce0a22f9f66c0e4..e0a81beb4f37751421dbbe794ccf3d5a46bdf900 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -278,22 +278,26 @@ static bool netlink_filter_tap(const struct sk_buff *skb)
        return false;
 }
 
-static int __netlink_deliver_tap_skb(struct sk_buff *skb,
+static int __netlink_deliver_tap_skb(struct sk_buff **pskb,
                                     struct net_device *dev)
 {
-       struct sk_buff *nskb;
+       struct sk_buff *nskb, *skb = *pskb;
        struct sock *sk = skb->sk;
        int ret = -ENOMEM;
 
        if (!net_eq(dev_net(dev), sock_net(sk)))
                return 0;
 
-       dev_hold(dev);
-
-       if (is_vmalloc_addr(skb->head))
+       if (is_vmalloc_addr(skb->head)) {
                nskb = netlink_to_full_skb(skb, GFP_ATOMIC);
-       else
-               nskb = skb_clone(skb, GFP_ATOMIC);
+               if (!nskb)
+                       return -ENOMEM;
+               consume_skb(skb);
+               skb = nskb;
+               *pskb = skb;
+       }
+       dev_hold(dev);
+       nskb = skb_clone(skb, GFP_ATOMIC);
        if (nskb) {
                nskb->dev = dev;
                nskb->protocol = htons((u16) sk->sk_protocol);
@@ -318,7 +322,7 @@ static void __netlink_deliver_tap(struct sk_buff *skb, struct netlink_tap_net *n
                return;
 
        list_for_each_entry_rcu(tmp, &nn->netlink_tap_all, list) {
-               ret = __netlink_deliver_tap_skb(skb, tmp->dev);
+               ret = __netlink_deliver_tap_skb(&skb, tmp->dev);
                if (unlikely(ret))
                        break;
        }