page_pool: check for PP direct cache locality later

Since we have pool->p.napi (Jakub) and pool->cpuid (Lorenzo) to check
whether it's safe to use direct recycling, we can use both globally for
each page instead of relying solely on @allow_direct argument.
Let's assume that @allow_direct means "I'm sure it's local, don't waste
time rechecking this" and when it's false, try the mentioned params to
still recycle the page directly. If neither is true, we'll lose some
CPU cycles, but then it surely won't be hotpath. On the other hand,
paths where it's possible to use direct cache, but not possible to
safely set @allow_direct, will benefit from this move.
The whole propagation of @napi_safe through a dozen of skb freeing
functions can now go away, which saves us some stack space.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://lore.kernel.org/r/20240329165507.3240110-2-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 22 insertions, 48 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a1be84be5d35..2a5ce6667bbb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1004,11 +1004,8 @@ int skb_cow_data_for_xdp(struct page_pool *pool, struct sk_buff **pskb,
 EXPORT_SYMBOL(skb_cow_data_for_xdp);
 
 #if IS_ENABLED(CONFIG_PAGE_POOL)
-bool napi_pp_put_page(struct page *page, bool napi_safe)
+bool napi_pp_put_page(struct page *page)
 {
-	bool allow_direct = false;
-	struct page_pool *pp;
-
 	page = compound_head(page);
 
 	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
@@ -1021,39 +1018,18 @@ bool napi_pp_put_page(struct page *page, bool napi_safe)
 	if (unlikely(!is_pp_page(page)))
 		return false;
 
-	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.
-	 * __page_pool_put_page() makes sure we're not in hardirq context
-	 * and interrupts are enabled prior to accessing the cache.
-	 */
-	if (napi_safe || in_softirq()) {
-		const struct napi_struct *napi = READ_ONCE(pp->p.napi);
-		unsigned int cpuid = smp_processor_id();
-
-		allow_direct = napi && READ_ONCE(napi->list_owner) == cpuid;
-		allow_direct |= READ_ONCE(pp->cpuid) == cpuid;
-	}
-
-	/* 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, allow_direct);
+	page_pool_put_full_page(page->pp, page, false);
 
 	return true;
 }
 EXPORT_SYMBOL(napi_pp_put_page);
 #endif
 
-static bool skb_pp_recycle(struct sk_buff *skb, void *data, bool napi_safe)
+static bool skb_pp_recycle(struct sk_buff *skb, void *data)
 {
 	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
 		return false;
-	return napi_pp_put_page(virt_to_page(data), napi_safe);
+	return napi_pp_put_page(virt_to_page(data));
 }
 
 /**
@@ -1095,12 +1071,12 @@ static void skb_kfree_head(void *head, unsigned int end_offset)
 		kfree(head);
 }
 
-static void skb_free_head(struct sk_buff *skb, bool napi_safe)
+static void skb_free_head(struct sk_buff *skb)
 {
 	unsigned char *head = skb->head;
 
 	if (skb->head_frag) {
-		if (skb_pp_recycle(skb, head, napi_safe))
+		if (skb_pp_recycle(skb, head))
 			return;
 		skb_free_frag(head);
 	} else {
@@ -1108,8 +1084,7 @@ static void skb_free_head(struct sk_buff *skb, bool napi_safe)
 	}
 }
 
-static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason,
-			     bool napi_safe)
+static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
 	int i;
@@ -1126,13 +1101,13 @@ static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason,
 	}
 
 	for (i = 0; i < shinfo->nr_frags; i++)
-		napi_frag_unref(&shinfo->frags[i], skb->pp_recycle, napi_safe);
+		napi_frag_unref(&shinfo->frags[i], skb->pp_recycle);
 
 free_head:
 	if (shinfo->frag_list)
 		kfree_skb_list_reason(shinfo->frag_list, reason);
 
-	skb_free_head(skb, napi_safe);
+	skb_free_head(skb);
 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
@@ -1193,12 +1168,11 @@ 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,
-			    bool napi_safe)
+static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)
 {
 	skb_release_head_state(skb);
 	if (likely(skb->head))
-		skb_release_data(skb, reason, napi_safe);
+		skb_release_data(skb, reason);
 }
 
 /**
@@ -1212,7 +1186,7 @@ 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, false);
+	skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
 	kfree_skbmem(skb);
 }
 EXPORT_SYMBOL(__kfree_skb);
@@ -1269,7 +1243,7 @@ static void kfree_skb_add_bulk(struct sk_buff *skb,
 		return;
 	}
 
-	skb_release_all(skb, reason, false);
+	skb_release_all(skb, reason);
 	sa->skb_array[sa->skb_count++] = skb;
 
 	if (unlikely(sa->skb_count == KFREE_SKB_BULK_SIZE)) {
@@ -1443,7 +1417,7 @@ 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, false);
+	skb_release_data(skb, SKB_CONSUMED);
 	kfree_skbmem(skb);
 }
 
@@ -1470,7 +1444,7 @@ static void napi_skb_cache_put(struct sk_buff *skb)
 
 void __napi_kfree_skb(struct sk_buff *skb, enum skb_drop_reason reason)
 {
-	skb_release_all(skb, reason, true);
+	skb_release_all(skb, reason);
 	napi_skb_cache_put(skb);
 }
 
@@ -1508,7 +1482,7 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 		return;
 	}
 
-	skb_release_all(skb, SKB_CONSUMED, !!budget);
+	skb_release_all(skb, SKB_CONSUMED);
 	napi_skb_cache_put(skb);
 }
 EXPORT_SYMBOL(napi_consume_skb);
@@ -1639,7 +1613,7 @@ 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, false);
+	skb_release_all(dst, SKB_CONSUMED);
 	return __skb_clone(dst, src);
 }
 EXPORT_SYMBOL_GPL(skb_morph);
@@ -2271,9 +2245,9 @@ 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, false);
+		skb_release_data(skb, SKB_CONSUMED);
 	} else {
-		skb_free_head(skb, false);
+		skb_free_head(skb);
 	}
 	off = (data + nhead) - skb->head;
 
@@ -6574,12 +6548,12 @@ 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, false);
+		skb_release_data(skb, SKB_CONSUMED);
 	} else {
 		/* we can reuse existing recount- all we did was
 		 * relocate values
 		 */
-		skb_free_head(skb, false);
+		skb_free_head(skb);
 	}
 
 	skb->head = data;
@@ -6714,7 +6688,7 @@ 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, false);
+	skb_release_data(skb, SKB_CONSUMED);
 
 	skb->head = data;
 	skb->head_frag = 0;