Re: [PATCH net-next v4 2/4] page_pool: Allow drivers to hint on SKB recycling

[Eric Dumazet <eric.dumazet@gmail.com>]

On 5/11/21 3:31 PM, Matteo Croce wrote:
> From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> 
> Up to now several high speed NICs have custom mechanisms of recycling
> the allocated memory they use for their payloads.
> Our page_pool API already has recycling capabilities that are always
> used when we are running in 'XDP mode'. So let's tweak the API and the
> kernel network stack slightly and allow the recycling to happen even
> during the standard operation.
> The API doesn't take into account 'split page' policies used by those
> drivers currently, but can be extended once we have users for that.
> 
> The idea is to be able to intercept the packet on skb_release_data().
> If it's a buffer coming from our page_pool API recycle it back to the
> pool for further usage or just release the packet entirely.
> 
> To achieve that we introduce a bit in struct sk_buff (pp_recycle:1) and
> store the page_pool pointer in page->private. Storing the information in
> page->private allows us to recycle both SKBs and their fragments.
> The SKB bit is needed for a couple of reasons. First of all in an
> effort to affect the free path as less as possible, reading a single bit,
> is better that trying to derive identical information for the page stored
> data. Moreover page->private is used by skb_copy_ubufs. We do have a
> special mark in the page, that won't allow this to happen, but again
> deciding without having to read the entire page is preferable.
> 
> The driver has to take care of the sync operations on it's own
> during the buffer recycling since the buffer is, after opting-in to the
> recycling, never unmapped.
> 
> Since the gain on the drivers depends on the architecture, we are not
> enabling recycling by default if the page_pool API is used on a driver.
> In order to enable recycling the driver must call skb_mark_for_recycle()
> to store the information we need for recycling in page->private and
> enabling the recycling bit, or page_pool_store_mem_info() for a fragment.
> 
> Since we added an extra argument on __skb_frag_unref() to handle
> recycling, update the current users of the function with that.

This part could be done with a preliminary patch, only adding this
extra boolean, this would keep the 'complex' patch smaller.

> 
> Co-developed-by: Jesper Dangaard Brouer <brouer@redhat.com>
> Co-developed-by: Matteo Croce <mcroce@microsoft.com>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> Signed-off-by: Matteo Croce <mcroce@microsoft.com>
> ---
>  drivers/net/ethernet/marvell/sky2.c        |  2 +-
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c |  2 +-
>  include/linux/skbuff.h                     | 34 ++++++++++++++++++----
>  include/net/page_pool.h                    |  9 ++++++
>  net/core/page_pool.c                       | 23 +++++++++++++++
>  net/core/skbuff.c                          | 20 +++++++++++--
>  net/tls/tls_device.c                       |  2 +-
>  7 files changed, 82 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/sky2.c b/drivers/net/ethernet/marvell/sky2.c
> index 222c32367b2c..aa0cde1dc5c0 100644
> --- a/drivers/net/ethernet/marvell/sky2.c
> +++ b/drivers/net/ethernet/marvell/sky2.c
> @@ -2503,7 +2503,7 @@ static void skb_put_frags(struct sk_buff *skb, unsigned int hdr_space,
>  
>  		if (length == 0) {
>  			/* don't need this page */
> -			__skb_frag_unref(frag);
> +			__skb_frag_unref(frag, false);
>  			--skb_shinfo(skb)->nr_frags;
>  		} else {
>  			size = min(length, (unsigned) PAGE_SIZE);
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index e35e4d7ef4d1..cea62b8f554c 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -526,7 +526,7 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv,
>  fail:
>  	while (nr > 0) {
>  		nr--;
> -		__skb_frag_unref(skb_shinfo(skb)->frags + nr);
> +		__skb_frag_unref(skb_shinfo(skb)->frags + nr, false);
>  	}
>  	return 0;
>  }
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index dbf820a50a39..1a2ce52c29f9 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
> +#if IS_BUILTIN(CONFIG_PAGE_POOL)
> +#include <net/page_pool.h>
> +#endif
>  
>  /* The interface for checksum offload between the stack and networking drivers
>   * is as follows...
> @@ -667,6 +670,8 @@ typedef unsigned char *sk_buff_data_t;
>   *	@head_frag: skb was allocated from page fragments,
>   *		not allocated by kmalloc() or vmalloc().
>   *	@pfmemalloc: skbuff was allocated from PFMEMALLOC reserves
> + *	@pp_recycle: mark the packet for recycling instead of freeing (implies
> + *		page_pool support on driver)
>   *	@active_extensions: active extensions (skb_ext_id types)
>   *	@ndisc_nodetype: router type (from link layer)
>   *	@ooo_okay: allow the mapping of a socket to a queue to be changed
> @@ -791,10 +796,12 @@ struct sk_buff {
>  				fclone:2,
>  				peeked:1,
>  				head_frag:1,
> -				pfmemalloc:1;
> +				pfmemalloc:1,
> +				pp_recycle:1; /* page_pool recycle indicator */
>  #ifdef CONFIG_SKB_EXTENSIONS
>  	__u8			active_extensions;
>  #endif
> +
>  	/* fields enclosed in headers_start/headers_end are copied
>  	 * using a single memcpy() in __copy_skb_header()
>  	 */
> @@ -3081,12 +3088,20 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
>  /**
>   * __skb_frag_unref - release a reference on a paged fragment.
>   * @frag: the paged fragment
> + * @recycle: recycle the page if allocated via page_pool
>   *
> - * Releases a reference on the paged fragment @frag.
> + * Releases a reference on the paged fragment @frag
> + * or recycles the page via the page_pool API.
>   */
> -static inline void __skb_frag_unref(skb_frag_t *frag)
> +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);
> +
> +#if IS_BUILTIN(CONFIG_PAGE_POOL)
> +	if (recycle && page_pool_return_skb_page(page_address(page)))
> +		return;
> +#endif
> +	put_page(page);
>  }
>  
>  /**
> @@ -3098,7 +3113,7 @@ static inline void __skb_frag_unref(skb_frag_t *frag)
>   */
>  static inline void skb_frag_unref(struct sk_buff *skb, int f)
>  {
> -	__skb_frag_unref(&skb_shinfo(skb)->frags[f]);
> +	__skb_frag_unref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
>  }
>  
>  /**
> @@ -4697,5 +4712,14 @@ static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
>  #endif
>  }
>  
> +#if IS_BUILTIN(CONFIG_PAGE_POOL)
> +static inline void skb_mark_for_recycle(struct sk_buff *skb, struct page *page,
> +					struct page_pool *pp)
> +{
> +	skb->pp_recycle = 1;
> +	page_pool_store_mem_info(page, pp);
> +}
> +#endif
> +
>  #endif	/* __KERNEL__ */
>  #endif	/* _LINUX_SKBUFF_H */
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 9814e36becc1..b34b8b128206 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -148,6 +148,8 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool)
>  	return pool->p.dma_dir;
>  }
>  
> +bool page_pool_return_skb_page(void *data);
> +
>  struct page_pool *page_pool_create(const struct page_pool_params *params);
>  
>  #ifdef CONFIG_PAGE_POOL
> @@ -253,4 +255,11 @@ 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)
> +{
> +	set_page_private(page, (unsigned long)pp);
> +}
> +
>  #endif /* _NET_PAGE_POOL_H */
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 2e5e2b8c3a02..52e4f16b5e92 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -626,3 +626,26 @@ 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->signature != PP_SIGNATURE))
> +		return false;
> +
> +	pp = (struct page_pool *)page_private(page);
> +
> +	/* 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.
> +	 */
> +	set_page_private(page, 0);
> +	page_pool_put_full_page(pp, virt_to_head_page(data), false);
> +
> +	return true;
> +}
> +EXPORT_SYMBOL(page_pool_return_skb_page);
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3ad22870298c..dc4a5c56b8dc 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>
> +#if IS_BUILTIN(CONFIG_PAGE_POOL)
> +#include <net/page_pool.h>
> +#endif
>  
>  #include <linux/uaccess.h>
>  #include <trace/events/skb.h>
> @@ -645,6 +648,11 @@ static void skb_free_head(struct sk_buff *skb)
>  {
>  	unsigned char *head = skb->head;
>  
> +#if IS_BUILTIN(CONFIG_PAGE_POOL)

Why IS_BUILTIN() ? 

PAGE_POOL is either y or n

IS_ENABLED() would look better, since we use IS_BUILTIN() for the cases where a module might be used.

Or simply #ifdef CONFIG_PAGE_POOL

> +	if (skb->pp_recycle && page_pool_return_skb_page(head))

This probably should be attempted only in the (skb->head_frag) case ?

Also this patch misses pskb_expand_head()

> +		return;
> +#endif
> +
>  	if (skb->head_frag)
>  		skb_free_frag(head);
>  	else
> @@ -664,7 +672,7 @@ static void skb_release_data(struct sk_buff *skb)
>  	skb_zcopy_clear(skb, true);
>  
>  	for (i = 0; i < shinfo->nr_frags; i++)
> -		__skb_frag_unref(&shinfo->frags[i]);
> +		__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
>  
>  	if (shinfo->frag_list)
>  		kfree_skb_list(shinfo->frag_list);
> @@ -1046,6 +1054,7 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
>  	n->nohdr = 0;
>  	n->peeked = 0;
>  	C(pfmemalloc);
> +	C(pp_recycle);
>  	n->destructor = NULL;
>  	C(tail);
>  	C(end);
> @@ -3495,7 +3504,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
>  		fragto = &skb_shinfo(tgt)->frags[merge];
>  
>  		skb_frag_size_add(fragto, skb_frag_size(fragfrom));
> -		__skb_frag_unref(fragfrom);
> +		__skb_frag_unref(fragfrom, skb->pp_recycle);
>  	}
>  
>  	/* Reposition in the original skb */
> @@ -5285,6 +5294,13 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
>  	if (skb_cloned(to))
>  		return false;
>  
> +	/* We can't coalesce skb that are allocated from slab and page_pool
> +	 * The recycle mark is on the skb, so that might end up trying to
> +	 * recycle slab allocated skb->head
> +	 */
> +	if (to->pp_recycle != from->pp_recycle)
> +		return false;
> +
>  	if (len <= skb_tailroom(to)) {
>  		if (len)
>  			BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
> diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
> index 76a6f8c2eec4..ad11db2c4f63 100644
> --- a/net/tls/tls_device.c
> +++ b/net/tls/tls_device.c
> @@ -127,7 +127,7 @@ static void destroy_record(struct tls_record_info *record)
>  	int i;
>  
>  	for (i = 0; i < record->num_frags; i++)
> -		__skb_frag_unref(&record->frags[i]);
> +		__skb_frag_unref(&record->frags[i], false);
>  	kfree(record);
>  }
>  
>