netdev - [PATCH net-next v2 2/4] net: Introduce {netdev,napi}_alloc_frag

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Message-Id: <20210131074426.44154-3-haokexin@gmail.com>
Date:   Sun, 31 Jan 2021 15:44:24 +0800
From:   Kevin Hao <haokexin@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next v2 2/4] net: Introduce {netdev,napi}_alloc_frag_align()

In the current implementation of {netdev,napi}_alloc_frag(), it doesn't
have any align guarantee for the returned buffer address, But for some
hardwares they do require the DMA buffer to be aligned correctly,
so we would have to use some workarounds like below if the buffers
allocated by the {netdev,napi}_alloc_frag() are used by these hardwares
for DMA.
    buf = napi_alloc_frag(really_needed_size + align);
    buf = PTR_ALIGN(buf, align);

These codes seems ugly and would waste a lot of memories if the buffers
are used in a network driver for the TX/RX. We have added the align
support for the page_frag functions, so add the corresponding
{netdev,napi}_frag functions.

Signed-off-by: Kevin Hao <haokexin@...il.com>
---
v2: Inline {netdev,napi}_alloc_frag().

 include/linux/skbuff.h | 22 ++++++++++++++++++++--
 net/core/skbuff.c      | 25 +++++++++----------------
 2 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9313b5aaf45b..7e8beff4ff22 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2818,7 +2818,19 @@ void skb_queue_purge(struct sk_buff_head *list);
 
 unsigned int skb_rbtree_purge(struct rb_root *root);
 
-void *netdev_alloc_frag(unsigned int fragsz);
+void *netdev_alloc_frag_align(unsigned int fragsz, int align);
+
+/**
+ * netdev_alloc_frag - allocate a page fragment
+ * @fragsz: fragment size
+ *
+ * Allocates a frag from a page for receive buffer.
+ * Uses GFP_ATOMIC allocations.
+ */
+static inline void *netdev_alloc_frag(unsigned int fragsz)
+{
+	return netdev_alloc_frag_align(fragsz, 0);
+}
 
 struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int length,
 				   gfp_t gfp_mask);
@@ -2877,7 +2889,13 @@ static inline void skb_free_frag(void *addr)
 	page_frag_free(addr);
 }
 
-void *napi_alloc_frag(unsigned int fragsz);
+void *napi_alloc_frag_align(unsigned int fragsz, int align);
+
+static inline void *napi_alloc_frag(unsigned int fragsz)
+{
+	return napi_alloc_frag_align(fragsz, 0);
+}
+
 struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
 				 unsigned int length, gfp_t gfp_mask);
 static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2af12f7e170c..a35e75f12428 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -374,29 +374,22 @@ struct napi_alloc_cache {
 static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
 static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache);
 
-static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
+static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask, int align)
 {
 	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
 
-	return page_frag_alloc(&nc->page, fragsz, gfp_mask);
+	return page_frag_alloc_align(&nc->page, fragsz, gfp_mask, align);
 }
 
-void *napi_alloc_frag(unsigned int fragsz)
+void *napi_alloc_frag_align(unsigned int fragsz, int align)
 {
 	fragsz = SKB_DATA_ALIGN(fragsz);
 
-	return __napi_alloc_frag(fragsz, GFP_ATOMIC);
+	return __napi_alloc_frag(fragsz, GFP_ATOMIC, align);
 }
-EXPORT_SYMBOL(napi_alloc_frag);
+EXPORT_SYMBOL(napi_alloc_frag_align);
 
-/**
- * netdev_alloc_frag - allocate a page fragment
- * @fragsz: fragment size
- *
- * Allocates a frag from a page for receive buffer.
- * Uses GFP_ATOMIC allocations.
- */
-void *netdev_alloc_frag(unsigned int fragsz)
+void *netdev_alloc_frag_align(unsigned int fragsz, int align)
 {
 	struct page_frag_cache *nc;
 	void *data;
@@ -404,15 +397,15 @@ void *netdev_alloc_frag(unsigned int fragsz)
 	fragsz = SKB_DATA_ALIGN(fragsz);
 	if (in_irq() || irqs_disabled()) {
 		nc = this_cpu_ptr(&netdev_alloc_cache);
-		data = page_frag_alloc(nc, fragsz, GFP_ATOMIC);
+		data = page_frag_alloc_align(nc, fragsz, GFP_ATOMIC, align);
 	} else {
 		local_bh_disable();
-		data = __napi_alloc_frag(fragsz, GFP_ATOMIC);
+		data = __napi_alloc_frag(fragsz, GFP_ATOMIC, align);
 		local_bh_enable();
 	}
 	return data;
 }
-EXPORT_SYMBOL(netdev_alloc_frag);
+EXPORT_SYMBOL(netdev_alloc_frag_align);
 
 /**
  *	__netdev_alloc_skb - allocate an skbuff for rx on a specific device
-- 
2.29.2