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Commit ce1a4ea3 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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net: avoid one atomic operation in skb_clone() 



Fast clone cloning can actually avoid an atomic_inc(), if we
guarantee prior clone_ref value is 1.

This requires a change kfree_skbmem(), to perform the
atomic_dec_and_test() on clone_ref before setting fclone to
SKB_FCLONE_UNAVAILABLE.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e500f488

net/core/skbuff.c

+17 −6
Original line number Original line Diff line number Diff line
@@ -541,13 +541,20 @@ static void kfree_skbmem(struct sk_buff *skb) 
	case SKB_FCLONE_CLONE:

	case SKB_FCLONE_CLONE:

		fclones = container_of(skb, struct sk_buff_fclones, skb2);

		fclones = container_of(skb, struct sk_buff_fclones, skb2);





		/* Warning : We must perform the atomic_dec_and_test() before

		 * setting skb->fclone back to SKB_FCLONE_UNAVAILABLE, otherwise

		 * skb_clone() could set clone_ref to 2 before our decrement.

		 * Anyway, if we are going to free the structure, no need to

		 * rewrite skb->fclone.

		 */

		if (atomic_dec_and_test(&fclones->fclone_ref)) {

			kmem_cache_free(skbuff_fclone_cache, fclones);

		} else {

			/* The clone portion is available for

			/* The clone portion is available for

			 * fast-cloning again.

			 * fast-cloning again.

			 */

			 */

			skb->fclone = SKB_FCLONE_UNAVAILABLE;

			skb->fclone = SKB_FCLONE_UNAVAILABLE;



		}

		if (atomic_dec_and_test(&fclones->fclone_ref))

			kmem_cache_free(skbuff_fclone_cache, fclones);

		break;

		break;

	}

	}

}

}
@@ -869,7 +876,11 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask) 
	if (skb->fclone == SKB_FCLONE_ORIG &&

	if (skb->fclone == SKB_FCLONE_ORIG &&

	    n->fclone == SKB_FCLONE_UNAVAILABLE) {

	    n->fclone == SKB_FCLONE_UNAVAILABLE) {

		n->fclone = SKB_FCLONE_CLONE;

		n->fclone = SKB_FCLONE_CLONE;

		atomic_inc(&fclones->fclone_ref);

		/* As our fastclone was free, clone_ref must be 1 at this point.

		 * We could use atomic_inc() here, but it is faster

		 * to set the final value.

		 */

		atomic_set(&fclones->fclone_ref, 2);

	} else {

	} else {

		if (skb_pfmemalloc(skb))

		if (skb_pfmemalloc(skb))

			gfp_mask |= __GFP_MEMALLOC;

			gfp_mask |= __GFP_MEMALLOC;