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Commit fed66381 authored Jul 22, 2010 by Eric Dumazet Committed by David S. Miller Jul 24, 2010

net: pskb_expand_head() optimization



Move frags[] at the end of struct skb_shared_info, and make
pskb_expand_head() copy only the used part of it instead of whole array.

This should avoid kmemcheck warnings and speedup pskb_expand_head() as
well, avoiding a lot of cache misses.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent c1f79426

include/linux/skbuff.h

+2 −1

Original line number	Original line	Diff line number	Diff line
	@@ -202,10 +202,11 @@ struct skb_shared_info {
	*/		*/
	atomic_t dataref;		atomic_t dataref;

	skb_frag_t frags[MAX_SKB_FRAGS];
	/* Intermediate layers must ensure that destructor_arg		/* Intermediate layers must ensure that destructor_arg
	* remains valid until skb destructor */		* remains valid until skb destructor */
	void * destructor_arg;		void * destructor_arg;
			/* must be last field, see pskb_expand_head() */
			skb_frag_t frags[MAX_SKB_FRAGS];
	};		};

	/* We divide dataref into two halves. The higher 16 bits hold references		/* We divide dataref into two halves. The higher 16 bits hold references

net/core/skbuff.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -817,7 +817,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
	memcpy(data + nhead, skb->head, skb->tail - skb->head);		memcpy(data + nhead, skb->head, skb->tail - skb->head);
	#endif		#endif
	memcpy(data + size, skb_end_pointer(skb),		memcpy(data + size, skb_end_pointer(skb),
	sizeof(struct skb_shared_info));		offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));

	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
	get_page(skb_shinfo(skb)->frags[i].page);		get_page(skb_shinfo(skb)->frags[i].page);