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| author | Eric Dumazet <edumazet@google.com> | 2014-10-02 00:27:15 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-10-02 03:27:23 +0200 |
| commit | ce1a4ea3f125863bfbcb1afb76590ee2b7b93fbf (patch) | |
| tree | 5efaaa29736600ab06f5c4ed27af855fb543de13 | |
| parent | net/dccp/ccid.c: add __init to ccid_activate (diff) | |
| download | linux-ce1a4ea3f125863bfbcb1afb76590ee2b7b93fbf.tar.xz linux-ce1a4ea3f125863bfbcb1afb76590ee2b7b93fbf.zip | |
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>
| -rw-r--r-- | net/core/skbuff.c | 23 |
1 files changed, 17 insertions, 6 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a8cebb40699c..f77e64873caf 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -541,13 +541,20 @@ static void kfree_skbmem(struct sk_buff *skb) case SKB_FCLONE_CLONE: fclones = container_of(skb, struct sk_buff_fclones, skb2); - /* The clone portion is available for - * fast-cloning again. + /* 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. */ - skb->fclone = SKB_FCLONE_UNAVAILABLE; - - if (atomic_dec_and_test(&fclones->fclone_ref)) + if (atomic_dec_and_test(&fclones->fclone_ref)) { kmem_cache_free(skbuff_fclone_cache, fclones); + } else { + /* The clone portion is available for + * fast-cloning again. + */ + skb->fclone = SKB_FCLONE_UNAVAILABLE; + } break; } } @@ -869,7 +876,11 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask) if (skb->fclone == SKB_FCLONE_ORIG && n->fclone == SKB_FCLONE_UNAVAILABLE) { 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 { if (skb_pfmemalloc(skb)) gfp_mask |= __GFP_MEMALLOC; |