netdev - Re: [PATCH net-next] tcp: Set rcv zerocopy hint correctly if skb last frag is < PAGE

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Date:   Sun, 15 Dec 2019 11:22:14 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Arjun Roy <arjunroy.kdev@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, arjunroy@...gle.com,
        soheil@...gle.com, edumazet@...gle.com
Subject: Re: [PATCH net-next] tcp: Set rcv zerocopy hint correctly if skb
 last frag is < PAGE_SIZE.

On Thu, 12 Dec 2019 14:59:30 -0800, Arjun Roy wrote:
> At present, if the last frag of paged data in a skb has < PAGE_SIZE
> data, we compute the recv_skip_hint as being equal to the size of that
> frag and the entire next skb.
> 
> Instead, just return the runt frag size as the hint.

nit: this commit message doesn't really tell us why or what the effects
     are going to be.

> Signed-off-by: Arjun Roy <arjunroy@...gle.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

WARNING: Missing Signed-off-by: line by nominal patch author 'Arjun Roy <arjunroy.kdev@...il.com>'

You gotta send it from the same address you signed it off from.
 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 34490d972758..b9623d896469 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1904,6 +1904,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
>  	while (length + PAGE_SIZE <= zc->length) {
>  		if (zc->recv_skip_hint < PAGE_SIZE) {
>  			if (skb) {
> +				if (zc->recv_skip_hint > 0)
> +					break;
>  				skb = skb->next;
>  				offset = seq - TCP_SKB_CB(skb)->seq;
>  			} else {