Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 04/06/14 09:50, David Laight wrote:
> From: netdev-owner@xxxxxxxxxxxxxxx
> > A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> > underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> > the next BUG_ON a few lines down, as the packet consumes more slots than
> > estimated.
> > This patch introduces full_coalesce on the skb callback buffer, which is used in
> > start_new_rx_buffer() to decide whether netback needs coalescing more
> > aggresively. By doing that, no packet should need more than
> > XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
> > utilized.
> ...
> > -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> > +static bool start_new_rx_buffer(int offset,
> > +                               unsigned long size,
> > +                               int head,
> > +                               bool full_coalesce)
> The above is completely incorrect layout ...
Can you elaborate a bit please on "above"?
> ...
> >         BUG_ON(size > MAX_BUFFER_OFFSET);
> > -       if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> > +       if ((offset + size > MAX_BUFFER_OFFSET) &&
> > +           offset &&
> > +           !head &&
> > +           !full_coalesce)
> >                 return true;
> As is that.
>
>         David
>
>
>
> --
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