Re: [PATCH 17/28] netvm: hook skb allocation to reserves

Andrew Morton
2008-02-23T08:20:42Z

On Wed, 20 Feb 2008 15:46:27 +0100 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Change the skb allocation api to indicate RX usage and use this to fall back to
> the reserve when needed. SKBs allocated from the reserve are tagged in
> skb->emergency.
>
> Teach all other skb ops about emergency skbs and the reserve accounting.
>
> Use the (new) packet split API to allocate and track fragment pages from the
> emergency reserve. Do this using an atomic counter in page->index. This is
> needed because the fragments have a different sharing semantic than that
> indicated by skb_shinfo()->dataref.
>
> Note that the decision to distinguish between regular and emergency SKBs allows
> the accounting overhead to be limited to the later kind.
>
> ...
>
> +static inline void skb_get_page(struct sk_buff *skb, struct page *page)
> +{
> + get_page(page);
> + if (skb_emergency(skb))
> + atomic_inc(&page->frag_count);
> +}
> +
> +static inline void skb_put_page(struct sk_buff *skb, struct page *page)
> +{
> + if (skb_emergency(skb) && atomic_dec_and_test(&page->frag_count))
> + rx_emergency_put(PAGE_SIZE);
> + put_page(page);
> +}

I'm thinking we should do `#define slowcall inline' then use that in the future.

> static void skb_release_data(struct sk_buff *skb)
> {
> if (!skb->cloned ||
> !atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
> &skb_shinfo(skb)->dataref)) {
> + int size;
> +
> +#ifdef NET_SKBUFF_DATA_USES_OFFSET
> + size = skb->end;
> +#else
> + size = skb->end - skb->head;
> +#endif

The patch adds rather a lot of ifdefs.