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: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -541,13 +541,20 @@ static void kfree_skbmem(struct sk_buff *skb)
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case SKB_FCLONE_CLONE:
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fclones = container_of(skb, struct sk_buff_fclones, skb2);
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/* The clone portion is available for
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* fast-cloning again.
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/* Warning : We must perform the atomic_dec_and_test() before
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* setting skb->fclone back to SKB_FCLONE_UNAVAILABLE, otherwise
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* skb_clone() could set clone_ref to 2 before our decrement.
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* Anyway, if we are going to free the structure, no need to
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* rewrite skb->fclone.
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*/
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skb->fclone = SKB_FCLONE_UNAVAILABLE;
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if (atomic_dec_and_test(&fclones->fclone_ref))
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if (atomic_dec_and_test(&fclones->fclone_ref)) {
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kmem_cache_free(skbuff_fclone_cache, fclones);
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} else {
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/* The clone portion is available for
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* fast-cloning again.
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*/
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skb->fclone = SKB_FCLONE_UNAVAILABLE;
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}
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break;
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}
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}
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@ -869,7 +876,11 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
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if (skb->fclone == SKB_FCLONE_ORIG &&
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n->fclone == SKB_FCLONE_UNAVAILABLE) {
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n->fclone = SKB_FCLONE_CLONE;
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atomic_inc(&fclones->fclone_ref);
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/* As our fastclone was free, clone_ref must be 1 at this point.
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* We could use atomic_inc() here, but it is faster
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* to set the final value.
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*/
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atomic_set(&fclones->fclone_ref, 2);
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} else {
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if (skb_pfmemalloc(skb))
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gfp_mask |= __GFP_MEMALLOC;
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