RE: PATCH zero-copy send completion callback

["Eric Barton" <eeb@bartonsoftware.com>]

> > Also, (please correct me if I'm wrong) I didn't
> > think this would push the allocation over to the next entry in
> > 'malloc_sizes'.
> 
> Well, skbuff heads are allocated from dedicated kmem_cache 
> (skbuff_fclone_cache & skbuff_head_cache), and these caches are not 
> constrained by the sizes available in malloc_sizes. Their 
> size are a multiple 
> of L1 CACHE size, which is 64 bytes for most common machines.

Indeed, struct skbuff is so allocated.  But I added the callback
pointers to struct skb_shared_info where the page pointers are stored,
and this struct is allocated along with the packet header using kmalloc.

> Even if your two pointers addition (16 bytes on x86_64) 
> doesnt cross a 64bytes 
> line (I didn't checked), they are going to be set to NULL 
> each time a skbuff 
> is allocated , and checked against NULL each time a skbuff is 
> destroyed.

Indeed.  Do you think that's significant?

                Cheers,
                        Eric

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