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

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

[Li RongQing]

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 using the first time allocated skb when iterate other devices
to send, reduce full allocation and speedup deliver.

Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 net/netlink/af_netlink.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index e3a0538ec0be..095b99e3c1fb 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -278,11 +278,11 @@ 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 **skb,
 				     struct net_device *dev)
 {
 	struct sk_buff *nskb;
-	struct sock *sk = skb->sk;
+	struct sock *sk = (*skb)->sk;
 	int ret = -ENOMEM;
 
 	if (!net_eq(dev_net(dev), sock_net(sk)))
@@ -290,10 +290,12 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb,
 
 	dev_hold(dev);
 
-	if (is_vmalloc_addr(skb->head))
-		nskb = netlink_to_full_skb(skb, GFP_ATOMIC);
+	if (is_vmalloc_addr((*skb)->head)) {
+		nskb = netlink_to_full_skb(*skb, GFP_ATOMIC);
+		*skb = nskb;
+	}
 	else
-		nskb = skb_clone(skb, GFP_ATOMIC);
+		nskb = skb_clone(*skb, GFP_ATOMIC);
 	if (nskb) {
 		nskb->dev = dev;
 		nskb->protocol = htons((u16) sk->sk_protocol);
@@ -318,7 +320,7 @@ 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;
 	}
-- 
2.16.2

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

[Eric Dumazet]

On 09/17/2018 10:26 PM, Li RongQing wrote:
> 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 using the first time allocated skb when iterate other devices
> to send, reduce full allocation and speedup deliver.
> 
> Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> ---
>  net/netlink/af_netlink.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
>

This looks very broken to me.

Only the original skb (given as an argument to __netlink_deliver_tap()) is guaranteed to not
disappear while the loop is performed.

(There is no skb_clone() after the first netlink_to_full_skb())

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

[Li,Rongqing]

> On 09/17/2018 10:26 PM, Li RongQing wrote:
> > if skb->head is vmalloc address, when this skb is delivered, full
> > allocation for this skb is required, if there are many devices, the
> > ---
> >  net/netlink/af_netlink.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> >
> >
> 
> This looks very broken to me.
> 
> Only the original skb (given as an argument to __netlink_deliver_tap()) is
> guaranteed to not disappear while the loop is performed.
> 
> (There is no skb_clone() after the first netlink_to_full_skb())
> 

Thank you;

I will rework it

-RongQing