netdev - Re: [PATCH net-next 3/3] udp: only use paged allocation with scatter-gather

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Date:   Mon, 14 May 2018 16:12:26 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next 3/3] udp: only use paged allocation with
 scatter-gather



On 05/14/2018 04:07 PM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> Paged allocation stores most payload in skb frags. This helps udp gso
> by avoiding copying from the gso skb to segment skb in skb_segment.
> 
> But without scatter-gather, data must be linear, so do not use paged
> mode unless NETIF_F_SG.
> 
> Fixes: 15e36f5b8e98 ("udp: paged allocation with gso")
> Reported-by: Sean Tranchetti <stranche@...eaurora.org>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/ipv4/ip_output.c  | 2 +-
>  net/ipv6/ip6_output.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index b5e21eb198d8..b38731d8a44f 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -884,7 +884,7 @@ static int __ip_append_data(struct sock *sk,
>  
>  	exthdrlen = !skb ? rt->dst.header_len : 0;
>  	mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;
> -	paged = !!cork->gso_size;
> +	paged = cork->gso_size && (rt->dst.dev->features & NETIF_F_SG);
>  
>  	if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
>  	    sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 7f4493080df6..35a940b9f208 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1262,7 +1262,7 @@ static int __ip6_append_data(struct sock *sk,
>  		dst_exthdrlen = rt->dst.header_len - rt->rt6i_nfheader_len;
>  	}
>  
> -	paged = !!cork->gso_size;
> +	paged = cork->gso_size && (rt->dst.dev->features & NETIF_F_SG);
>  	mtu = cork->gso_size ? IP6_MAX_MTU : cork->fragsize;
>  	orig_mtu = mtu;
>  
> 

As I said, this wont help for stacked device

bonding might advertise NETIF_F_SG, but one slave might not.