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

[David Laight <David.Laight@xxxxxxxxxx>]

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 ...

...
>       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




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel