On Mon, 30 Jul 2007 18:50:28 -0700 (PDT)
David Miller [off-list ref] wrote:

Stephen Rothwell pointed out to me that the skb_frag_struct
is broken on platforms using 64K or larger page sizes, it
even generates warnings when (for example) the myri10ge driver
tries to assign PAGE_SIZE into frag->size.

I've thus increased page offset and size to __u32 in the patch below.

I made this change much to even my own chagrin, but this is the
most direct fix and the ifdefs we could put here are both ugly
and also not something that we do with struct scatterlist so
no reason to do it in a place like this.

Actually, the cost on 64-bit is zero because there existed 4 bytes of
alignment padding for skb_frag_struct because of the page pointer.
On 32-bit the cost is up to 64-bytes :-/

Stephen, this opens up the doors a bit for the scatterlist work
you wanted to do in sk_buff.

Ouch... 

sizeof(struct skb_shared_info) is enlarged by 18*4 bytes on i386, a litle bit more than 64 bytes :(

I understand ifdefs are ugly, but in the common case (PAGE_SIZE<64K), this change seems very unfortunate.