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

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Date:   Tue, 18 Sep 2018 07:08:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Li RongQing <lirongqing@...du.com>, netdev@...r.kernel.org
Subject: Re: [PATCH][net-next] netlink: avoid to allocate full skb when
 sending to many devices



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@...du.com>
> Signed-off-by: Li RongQing <lirongqing@...du.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())