On Mon, 20 Aug 2012, Eric Dumazet wrote:
On Mon, 2012-08-20 at 08:18 +0200, Patrick McHardy wrote:
Add a function to allocate a skbuff head without any data. This will be
used by memory mapped netlink to attached data from the mmaped area to
the skb.
Additionally change skb_release_all() to check whether the skb has a
data area to allow the skb destructor to clear the data pointer in
case only a head has been allocated.
* ...
+struct sk_buff *__alloc_skb_head(gfp_t gfp_mask, int node)
+{
+ struct sk_buff *skb;
+
+ /* Get the HEAD */
+ skb = kmem_cache_alloc_node(skbuff_head_cache,
+ gfp_mask & ~__GFP_DMA, node);
+ if (!skb)
+ goto out;
+ prefetchw(skb);
+
This prefetch is probably not worth it, since you write on skb on the
following memset(). Cpu wont have enough 'time' to take benefit from
this hint.
Right, I remember we talked about that before and I already removed it.
Must have forgotten to actually commit that change, thanks!
+ /*
+ * Only clear those fields we need to clear, not those that we will
+ * actually initialise below. Hence, don't put any more fields after
+ * the tail pointer in struct sk_buff!
+ */
+ memset(skb, 0, offsetof(struct sk_buff, tail));
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