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authorEric Dumazet <edumazet@google.com>2014-10-02 02:27:15 +0400
committerDavid S. Miller <davem@davemloft.net>2014-10-02 05:27:23 +0400
commitce1a4ea3f125863bfbcb1afb76590ee2b7b93fbf (patch)
tree5efaaa29736600ab06f5c4ed27af855fb543de13 /net/core
parente500f488c27659bb6f5d313b336621f3daa67701 (diff)
downloadlinux-ce1a4ea3f125863bfbcb1afb76590ee2b7b93fbf.tar.xz
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>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/skbuff.c23
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;