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

From: Zoltan Kiss <[email-masked]>
Date: Wed, 4 Jun 2014 16:53:18 +0100

On 04/06/14 11:15, Zoltan Kiss wrote:
> On 04/06/14 09:50, David Laight wrote:
>> From: [email-masked]
>>> 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"?

I just realized you're not talking about skb layout but format. I'll fix 
that.

Zoli