Re: [PATCH net-next v7 3/5] page_pool: Allow drivers to hint on SKB recycling

[Ilias Apalodimas]

On Fri, Jun 04, 2021 at 08:41:52PM +0100, Matthew Wilcox wrote:
> 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?

I think we can. I'll check and change it. 

> 
> > @@ -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()?
> 

Sure, sounds reasonable. 

> > @@ -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.
> 

True

> > +	/* 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);
> > +	}
> >  }
> >  

ok


Thanks for having a look

Cheers
/Ilias