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.
> + /*
> + * 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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