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

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
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
-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.


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