Re: [Xen-devel] [PATCH RFC] tcp: Allow sk_wmem_alloc to exceed sysctl_tcp_limit_output_bytes

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

On Mon, 2015-04-13 at 14:46 +0100, David Vrabel wrote:

> > And the proof-of-concept patch for idea (b) I used was:
> > 
> > @@ -552,6 +552,8 @@ static int xennet_start_xmit(struct sk_buff *skb,
> > struct net_device *dev)
> >              goto drop;
> >      }
> > 
> > +    skb_orphan(skb);
> > +
> >      page = virt_to_page(skb->data);
> >      offset = offset_in_page(skb->data);
> >      len = skb_headlen(skb);
> 
> No. This a bunch of allocations and  a full memcpy of all the frags.

skb_orphan() does nothing like that.

But the main concern here is it basically breaks back pressure.

And you do not want this, unless there is no other choice.



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