[PATCH 12/14] skbuff: optimise alloc_skb_with_frags()

[Pavel Begunkov]

Many users of alloc_skb_with_frags() pass zero datalen, e.g.
all callers sock_alloc_send_skb() including udp. Extract and inline a
part of it doing skb allocation. BTW, do a minor cleanup, e.g. don't
set errcode in advance as it can't be optimised.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 include/linux/skbuff.h | 41 ++++++++++++++++++++++++++++++++++++-----
 net/core/skbuff.c      | 31 ++++++++++++-------------------
 2 files changed, 48 insertions(+), 24 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7fd2b44aada0..8ea145101b56 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1130,11 +1130,42 @@ static inline struct sk_buff *alloc_skb(unsigned int size,
 	return __alloc_skb(size, priority, 0, NUMA_NO_NODE);
 }
 
-struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
-				     unsigned long data_len,
-				     int max_page_order,
-				     int *errcode,
-				     gfp_t gfp_mask);
+struct sk_buff *alloc_skb_frags(struct sk_buff *skb,
+				unsigned long data_len,
+				int max_page_order,
+				int *errcode,
+				gfp_t gfp_mask);
+
+/**
+ * alloc_skb_with_frags - allocate skb with page frags
+ *
+ * @header_len: size of linear part
+ * @data_len: needed length in frags
+ * @max_page_order: max page order desired.
+ * @errcode: pointer to error code if any
+ * @gfp_mask: allocation mask
+ *
+ * This can be used to allocate a paged skb, given a maximal order for frags.
+ */
+static inline struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
+						   unsigned long data_len,
+						   int max_page_order,
+						   int *errcode,
+						   gfp_t gfp_mask)
+{
+	struct sk_buff *skb;
+
+	skb = alloc_skb(header_len, gfp_mask);
+	if (unlikely(!skb)) {
+		*errcode = -ENOBUFS;
+		return NULL;
+	}
+
+	if (!data_len)
+		return skb;
+	return alloc_skb_frags(skb, data_len, max_page_order, errcode, gfp_mask);
+}
+
 struct sk_buff *alloc_skb_for_msg(struct sk_buff *first);
 
 /* Layout of fast clones : [skb1][skb2][fclone_ref] */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a9b8ac38dc1a..7811dde22f26 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5922,40 +5922,32 @@ int skb_mpls_dec_ttl(struct sk_buff *skb)
 EXPORT_SYMBOL_GPL(skb_mpls_dec_ttl);
 
 /**
- * alloc_skb_with_frags - allocate skb with page frags
+ * alloc_skb_frags - allocate page frags for skb
  *
- * @header_len: size of linear part
+ * @skb: buffer
  * @data_len: needed length in frags
  * @max_page_order: max page order desired.
  * @errcode: pointer to error code if any
  * @gfp_mask: allocation mask
  *
- * This can be used to allocate a paged skb, given a maximal order for frags.
+ * This can be used to allocate pages for skb, given a maximal order for frags.
  */
-struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
-				     unsigned long data_len,
-				     int max_page_order,
-				     int *errcode,
-				     gfp_t gfp_mask)
+struct sk_buff *alloc_skb_frags(struct sk_buff *skb,
+				unsigned long data_len,
+				int max_page_order,
+				int *errcode,
+				gfp_t gfp_mask)
 {
 	int npages = (data_len + (PAGE_SIZE - 1)) >> PAGE_SHIFT;
 	unsigned long chunk;
-	struct sk_buff *skb;
 	struct page *page;
 	int i;
 
-	*errcode = -EMSGSIZE;
 	/* Note this test could be relaxed, if we succeed to allocate
 	 * high order pages...
 	 */
-	if (npages > MAX_SKB_FRAGS)
-		return NULL;
-
-	*errcode = -ENOBUFS;
-	skb = alloc_skb(header_len, gfp_mask);
-	if (!skb)
-		return NULL;
-
+	if (unlikely(npages > MAX_SKB_FRAGS))
+		goto failure;
 	skb->truesize += npages << PAGE_SHIFT;
 
 	for (i = 0; npages > 0; i++) {
@@ -5989,9 +5981,10 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
 
 failure:
 	kfree_skb(skb);
+	*errcode = -EMSGSIZE;
 	return NULL;
 }
-EXPORT_SYMBOL(alloc_skb_with_frags);
+EXPORT_SYMBOL(alloc_skb_frags);
 
 /* carve out the first off bytes from skb when off < headlen */
 static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
-- 
2.34.1