netdev - Re: [PATCH net-next] skbuff: optimize the pull_pages code in __pskb_pull

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Date:   Thu, 06 Jul 2017 02:23:23 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Lin Zhang <xiaolou4617@...il.com>
Cc:     davem@...emloft.net, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] skbuff: optimize the pull_pages code in
 __pskb_pull_tail()

On Thu, 2017-07-06 at 02:16 -0700, Eric Dumazet wrote:
> On Thu, 2017-07-06 at 17:01 +0800, Lin Zhang wrote:
> > In the pull_pages code block, if the first frags size > eat,
> > we can end the loop in advance to avoid extra copy.
> > 
> > Signed-off-by: Lin Zhang <xiaolou4617@...il.com>
> > ---
> >  net/core/skbuff.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index f990eb8..c00a1df 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -1720,6 +1720,10 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta)
> >  				skb_shinfo(skb)->frags[k].page_offset += eat;
> >  				skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
> >  				eat = 0;
> > +				if (!i) {
> > +					k = skb_shinfo(skb)->nr_frags;
> > +					break;
> > +				}
> >  			}
> >  			k++;
> >  		}
> 
> 1) net-next is closed during merge window.
> 
> 2) This change is completely buggy.
>    How have you tested it exactly ???

Hmm... it looks like I was wrong, but 1) still applies ;)