Date:   Fri, 4 Jun 2021 20:41:52 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     netdev@...r.kernel.org, linux-mm@...ck.org,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
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        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v7 3/5] page_pool: Allow drivers to hint on SKB
 recycling

On Fri, Jun 04, 2021 at 08:33:47PM +0200, Matteo Croce wrote:
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 7fcfea7e7b21..057b40ad29bd 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -40,6 +40,9 @@
>  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
>  #include <linux/netfilter/nf_conntrack_common.h>
>  #endif
> +#ifdef CONFIG_PAGE_POOL
> +#include <net/page_pool.h>
> +#endif

I'm not a huge fan of conditional includes ... any reason to not include
it always?

> @@ -3088,7 +3095,13 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
>   */
>  static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
>  {
> -	put_page(skb_frag_page(frag));
> +	struct page *page = skb_frag_page(frag);
> +
> +#ifdef CONFIG_PAGE_POOL
> +	if (recycle && page_pool_return_skb_page(page_address(page)))
> +		return;

It feels weird to have a page here, convert it back to an address,
then convert it back to a head page in page_pool_return_skb_page().
How about passing 'page' here, calling compound_head() in
page_pool_return_skb_page() and calling virt_to_page() in skb_free_head()?

> @@ -251,4 +253,11 @@ static inline void page_pool_ring_unlock(struct page_pool *pool)
>  		spin_unlock_bh(&pool->ring.producer_lock);
>  }
>  
> +/* Store mem_info on struct page and use it while recycling skb frags */
> +static inline
> +void page_pool_store_mem_info(struct page *page, struct page_pool *pp)
> +{
> +	page->pp = pp;

I'm not sure this wrapper needs to exist.

> +}
> +
>  #endif /* _NET_PAGE_POOL_H */
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index e1321bc9d316..a03f48f45696 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -628,3 +628,26 @@ void page_pool_update_nid(struct page_pool *pool, int new_nid)
>  	}
>  }
>  EXPORT_SYMBOL(page_pool_update_nid);
> +
> +bool page_pool_return_skb_page(void *data)
> +{
> +	struct page_pool *pp;
> +	struct page *page;
> +
> +	page = virt_to_head_page(data);
> +	if (unlikely(page->pp_magic != PP_SIGNATURE))
> +		return false;
> +
> +	pp = (struct page_pool *)page->pp;

You don't need the cast any more.

> +	/* Driver set this to memory recycling info. Reset it on recycle.
> +	 * This will *not* work for NIC using a split-page memory model.
> +	 * The page will be returned to the pool here regardless of the
> +	 * 'flipped' fragment being in use or not.
> +	 */
> +	page->pp = NULL;
> +	page_pool_put_full_page(pp, page, false);
> +
> +	return true;
> +}
> +EXPORT_SYMBOL(page_pool_return_skb_page);
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 12b7e90dd2b5..f769f08e7b32 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -70,6 +70,9 @@
>  #include <net/xfrm.h>
>  #include <net/mpls.h>
>  #include <net/mptcp.h>
> +#ifdef CONFIG_PAGE_POOL
> +#include <net/page_pool.h>
> +#endif
>  
>  #include <linux/uaccess.h>
>  #include <trace/events/skb.h>
> @@ -645,10 +648,15 @@ static void skb_free_head(struct sk_buff *skb)
>  {
>  	unsigned char *head = skb->head;
>  
> -	if (skb->head_frag)
> +	if (skb->head_frag) {
> +#ifdef CONFIG_PAGE_POOL
> +		if (skb->pp_recycle && page_pool_return_skb_page(head))
> +			return;
> +#endif

put this in a header file:

static inline bool skb_pp_recycle(struct sk_buff *skb, void *data)
{
	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
		return false;
	return page_pool_return_skb_page(virt_to_page(data));
}

then this becomes:

	if (skb->head_frag) {
		if (skb_pp_recycle(skb, head))
			return;
>  		skb_free_frag(head);
> -	else
> +	} else {
>  		kfree(head);
> +	}
>  }
>  
>  static void skb_release_data(struct sk_buff *skb)

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