Re: [Xen-devel] [PATCH net-next v3 6/9] xen-netback: Handle guests with too many frags

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 08/01/14 13:54, Eric Dumazet wrote:
> On Wed, 2014-01-08 at 13:49 +0000, Zoltan Kiss wrote:
> > On 08/01/14 02:12, Eric Dumazet wrote:
> > > On Wed, 2014-01-08 at 00:10 +0000, Zoltan Kiss wrote:
> > >
> > > > +               if (skb_shinfo(skb)->frag_list) {
> > > > +                       nskb = skb_shinfo(skb)->frag_list;
> > > > +                       xenvif_fill_frags(vif, nskb, INVALID_PENDING_IDX);
> > > > +                       skb->len += nskb->len;
> > > > +                       skb->data_len += nskb->len;
> > > > +                       skb->truesize += nskb->truesize;
> > > > +                       skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> > > > +                       skb_shinfo(nskb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> > > > +                       vif->tx_zerocopy_sent += 2;
> > > > +                       nskb = skb;
> > > > +
> > > > +                       skb = skb_copy_expand(skb,
> > > > +                                       0,
> > > > +                                       0,
> > > > +                                       GFP_ATOMIC | __GFP_NOWARN);
> > > skb can be NULL here
> > Thanks, fixed that.
> BTW, I am not sure why you copy the skb.
>
> Is it to get rid of frag_list, and why ?
Yes, it is to get rid of the frag_list, just to be on the safe side. I'm 
not sure if it is normal to send a big skb with MAX_SKB_FRAGS frags plus 
an empty skb on the frag_list with one frag, so I just consolidate them 
here. This scenario shouldn't happen very often anyway, even guests 
which can send more than MAX_SKB_FRAGS slots tends to do it rarely.
Zoli


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