Merge branch 'page_pool-allow-caching-from-safely-localized-napi'

Jakub Kicinski says:

====================
page_pool: allow caching from safely localized NAPI

I went back to the explicit "are we in NAPI method", mostly
because I don't like having both around :( (even tho I maintain
that in_softirq() && !in_hardirq() is as safe, as softirqs do
not nest).

Still returning the skbs to a CPU, tho, not to the NAPI instance.
I reckon we could create a small refcounted struct per NAPI instance
which would allow sockets and other users so hold a persisent
and safe reference. But that's a bigger change, and I get 90+%
recycling thru the cache with just these patches (for RR and
streaming tests with 100% CPU use it's almost 100%).

Some numbers for streaming test with 100% CPU use (from previous version,
but really they perform the same):

		HW-GRO				page=page
		before		after		before		after
recycle:
cached:			0	138669686		0	150197505
cache_full:		0	   223391		0	    74582
ring:		138551933         9997191	149299454		0
ring_full: 		0             488	     3154	   127590
released_refcnt:	0		0		0		0

alloc:
fast:		136491361	148615710	146969587	150322859
slow:		     1772	     1799	      144	      105
slow_high_order:	0		0		0		0
empty:		     1772	     1799	      144	      105
refill:		  2165245	   156302	  2332880	     2128
waive:			0		0		0		0

v1: https://lore.kernel.org/all/20230411201800.596103-1-kuba@kernel.org/
rfcv2: https://lore.kernel.org/all/20230405232100.103392-1-kuba@kernel.org/
====================

Link: https://lore.kernel.org/r/20230413042605.895677-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/page_pool.rst

@@ -165,6 +165,7 @@ Registration
     pp_params.pool_size = DESC_NUM;
     pp_params.nid = NUMA_NO_NODE;
     pp_params.dev = priv->dev;
+    pp_params.napi = napi; /* only if locking is tied to NAPI */
     pp_params.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
     page_pool = page_pool_create(&pp_params);
 

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -3211,6 +3211,7 @@ static int bnxt_alloc_rx_page_pool(struct bnxt *bp,
 
 	pp.pool_size = bp->rx_ring_size;
 	pp.nid = dev_to_node(&bp->pdev->dev);
+	pp.napi = &rxr->bnapi->napi;
 	pp.dev = &bp->pdev->dev;
 	pp.dma_dir = DMA_BIDIRECTIONAL;
 

include/linux/netdevice.h

@@ -360,8 +360,11 @@ struct napi_struct {
 	unsigned long		gro_bitmask;
 	int			(*poll)(struct napi_struct *, int);
 #ifdef CONFIG_NETPOLL
+	/* CPU actively polling if netpoll is configured */
 	int			poll_owner;
 #endif
+	/* CPU on which NAPI has been scheduled for processing */
+	int			list_owner;
 	struct net_device	*dev;
 	struct gro_list		gro_hash[GRO_HASH_BUCKETS];
 	struct sk_buff		*skb;

include/linux/skbuff.h

@@ -3386,6 +3386,18 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
 	__skb_frag_ref(&skb_shinfo(skb)->frags[f]);
 }
 
+static inline void
+napi_frag_unref(skb_frag_t *frag, bool recycle, bool napi_safe)
+{
+	struct page *page = skb_frag_page(frag);
+
+#ifdef CONFIG_PAGE_POOL
+	if (recycle && page_pool_return_skb_page(page, napi_safe))
+		return;
+#endif
+	put_page(page);
+}
+
 /**
  * __skb_frag_unref - release a reference on a paged fragment.
  * @frag: the paged fragment
@@ -3396,13 +3408,7 @@ static inline void skb_frag_ref(struct sk_buff *skb, int f)
  */
 static inline void __skb_frag_unref(skb_frag_t *frag, bool recycle)
 {
-	struct page *page = skb_frag_page(frag);
-
-#ifdef CONFIG_PAGE_POOL
-	if (recycle && page_pool_return_skb_page(page))
-		return;
-#endif
-	put_page(page);
+	napi_frag_unref(frag, recycle, false);
 }
 
 /**

include/net/page_pool.h

@@ -77,6 +77,7 @@ struct page_pool_params {
 	unsigned int	pool_size;
 	int		nid;  /* Numa node id to allocate from pages from */
 	struct device	*dev; /* device, for DMA pre-mapping purposes */
+	struct napi_struct *napi; /* Sole consumer of pages, otherwise NULL */
 	enum dma_data_direction dma_dir; /* DMA mapping direction */
 	unsigned int	max_len; /* max DMA sync memory size */
 	unsigned int	offset;  /* DMA addr offset */
@@ -239,7 +240,7 @@ 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(struct page *page);
+bool page_pool_return_skb_page(struct page *page, bool napi_safe);
 
 struct page_pool *page_pool_create(const struct page_pool_params *params);
 

net/core/dev.c

@@ -4359,6 +4359,7 @@ static inline void ____napi_schedule(struct softnet_data *sd,
 	}
 
 	list_add_tail(&napi->poll_list, &sd->poll_list);
+	WRITE_ONCE(napi->list_owner, smp_processor_id());
 	/* If not called from net_rx_action()
 	 * we have to raise NET_RX_SOFTIRQ.
 	 */
@@ -6069,6 +6070,7 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 		list_del_init(&n->poll_list);
 		local_irq_restore(flags);
 	}
+	WRITE_ONCE(n->list_owner, -1);
 
 	val = READ_ONCE(n->state);
 	do {
@@ -6384,6 +6386,7 @@ void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
 #ifdef CONFIG_NETPOLL
 	napi->poll_owner = -1;
 #endif
+	napi->list_owner = -1;
 	set_bit(NAPI_STATE_SCHED, &napi->state);
 	set_bit(NAPI_STATE_NPSVC, &napi->state);
 	list_add_rcu(&napi->dev_list, &dev->napi_list);

net/core/page_pool.c

@@ -19,6 +19,7 @@
 #include <linux/mm.h> /* for put_page() */
 #include <linux/poison.h>
 #include <linux/ethtool.h>
+#include <linux/netdevice.h>
 
 #include <trace/events/page_pool.h>
 
@@ -874,9 +875,11 @@ void page_pool_update_nid(struct page_pool *pool, int new_nid)
 }
 EXPORT_SYMBOL(page_pool_update_nid);
 
-bool page_pool_return_skb_page(struct page *page)
+bool page_pool_return_skb_page(struct page *page, bool napi_safe)
 {
+	struct napi_struct *napi;
 	struct page_pool *pp;
+	bool allow_direct;
 
 	page = compound_head(page);
 
@@ -892,12 +895,20 @@ bool page_pool_return_skb_page(struct page *page)
 
 	pp = page->pp;
 
+	/* Allow direct recycle if we have reasons to believe that we are
+	 * in the same context as the consumer would run, so there's
+	 * no possible race.
+	 */
+	napi = pp->p.napi;
+	allow_direct = napi_safe && napi &&
+		READ_ONCE(napi->list_owner) == smp_processor_id();
+
 	/* 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_pool_put_full_page(pp, page, false);
+	page_pool_put_full_page(pp, page, allow_direct);
 
 	return true;
 }

net/core/skbuff.c

@@ -839,11 +839,11 @@ static void skb_clone_fraglist(struct sk_buff *skb)
 		skb_get(list);
 }
 
-static bool skb_pp_recycle(struct sk_buff *skb, void *data)
+static bool skb_pp_recycle(struct sk_buff *skb, void *data, bool napi_safe)
 {
 	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
 		return false;
-	return page_pool_return_skb_page(virt_to_page(data));
+	return page_pool_return_skb_page(virt_to_page(data), napi_safe);
 }
 
 static void skb_kfree_head(void *head, unsigned int end_offset)
@@ -856,12 +856,12 @@ static void skb_kfree_head(void *head, unsigned int end_offset)
 		kfree(head);
 }
 
-static void skb_free_head(struct sk_buff *skb)
+static void skb_free_head(struct sk_buff *skb, bool napi_safe)
 {
 	unsigned char *head = skb->head;
 
 	if (skb->head_frag) {
-		if (skb_pp_recycle(skb, head))
+		if (skb_pp_recycle(skb, head, napi_safe))
 			return;
 		skb_free_frag(head);
 	} else {
@@ -869,7 +869,8 @@ static void skb_free_head(struct sk_buff *skb)
 	}
 }
 
-static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
+static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason,
+			     bool napi_safe)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
 	int i;
@@ -888,13 +889,13 @@ static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
 	}
 
 	for (i = 0; i < shinfo->nr_frags; i++)
-		__skb_frag_unref(&shinfo->frags[i], skb->pp_recycle);
+		napi_frag_unref(&shinfo->frags[i], skb->pp_recycle, napi_safe);
 
 free_head:
 	if (shinfo->frag_list)
 		kfree_skb_list_reason(shinfo->frag_list, reason);
 
-	skb_free_head(skb);
+	skb_free_head(skb, napi_safe);
 exit:
 	/* When we clone an SKB we copy the reycling bit. The pp_recycle
 	 * bit is only set on the head though, so in order to avoid races
@@ -955,11 +956,12 @@ void skb_release_head_state(struct sk_buff *skb)
 }
 
 /* Free everything but the sk_buff shell. */
-static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)
+static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason,
+			    bool napi_safe)
 {
 	skb_release_head_state(skb);
 	if (likely(skb->head))
-		skb_release_data(skb, reason);
+		skb_release_data(skb, reason, napi_safe);
 }
 
 /**
@@ -973,7 +975,7 @@ static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)
 
 void __kfree_skb(struct sk_buff *skb)
 {
-	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED, false);
 	kfree_skbmem(skb);
 }
 EXPORT_SYMBOL(__kfree_skb);
@@ -1027,7 +1029,7 @@ static void kfree_skb_add_bulk(struct sk_buff *skb,
 		return;
 	}
 
-	skb_release_all(skb, reason);
+	skb_release_all(skb, reason, false);
 	sa->skb_array[sa->skb_count++] = skb;
 
 	if (unlikely(sa->skb_count == KFREE_SKB_BULK_SIZE)) {
@@ -1201,7 +1203,7 @@ EXPORT_SYMBOL(consume_skb);
 void __consume_stateless_skb(struct sk_buff *skb)
 {
 	trace_consume_skb(skb, __builtin_return_address(0));
-	skb_release_data(skb, SKB_CONSUMED);
+	skb_release_data(skb, SKB_CONSUMED, false);
 	kfree_skbmem(skb);
 }
 
@@ -1226,7 +1228,7 @@ static void napi_skb_cache_put(struct sk_buff *skb)
 
 void __kfree_skb_defer(struct sk_buff *skb)
 {
-	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED, true);
 	napi_skb_cache_put(skb);
 }
 
@@ -1264,7 +1266,7 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 		return;
 	}
 
-	skb_release_all(skb, SKB_CONSUMED);
+	skb_release_all(skb, SKB_CONSUMED, !!budget);
 	napi_skb_cache_put(skb);
 }
 EXPORT_SYMBOL(napi_consume_skb);
@@ -1395,7 +1397,7 @@ EXPORT_SYMBOL_GPL(alloc_skb_for_msg);
  */
 struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
 {
-	skb_release_all(dst, SKB_CONSUMED);
+	skb_release_all(dst, SKB_CONSUMED, false);
 	return __skb_clone(dst, src);
 }
 EXPORT_SYMBOL_GPL(skb_morph);
@@ -2018,9 +2020,9 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		if (skb_has_frag_list(skb))
 			skb_clone_fraglist(skb);
 
-		skb_release_data(skb, SKB_CONSUMED);
+		skb_release_data(skb, SKB_CONSUMED, false);
 	} else {
-		skb_free_head(skb);
+		skb_free_head(skb, false);
 	}
 	off = (data + nhead) - skb->head;
 
@@ -6389,12 +6391,12 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
 			skb_frag_ref(skb, i);
 		if (skb_has_frag_list(skb))
 			skb_clone_fraglist(skb);
-		skb_release_data(skb, SKB_CONSUMED);
+		skb_release_data(skb, SKB_CONSUMED, false);
 	} else {
 		/* we can reuse existing recount- all we did was
 		 * relocate values
 		 */
-		skb_free_head(skb);
+		skb_free_head(skb, false);
 	}
 
 	skb->head = data;
@@ -6529,7 +6531,7 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
 		skb_kfree_head(data, size);
 		return -ENOMEM;
 	}
-	skb_release_data(skb, SKB_CONSUMED);
+	skb_release_data(skb, SKB_CONSUMED, false);
 
 	skb->head = data;
 	skb->head_frag = 0;