net: allow alloc_skb_with_frags() to allocate bigger packets

Refactor alloc_skb_with_frags() to allow bigger packets allocations.

Instead of assuming that only order-0 allocations will be attempted,
use the caller supplied max order.

v2: try harder to use high-order pages, per Willem feedback.

Link: https://lore.kernel.org/netdev/CANn89iJQfmc_KeUr3TeXvsLQwo3ZymyoCr7Y6AnHrkWSuz0yAg@mail.gmail.com/Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tahsin Erdogan <trdgn@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20230801205254.400094-2-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/skbuff.c

@@ -6204,7 +6204,7 @@ EXPORT_SYMBOL_GPL(skb_mpls_dec_ttl);
  *
  * @header_len: size of linear part
  * @data_len: needed length in frags
- * @max_page_order: max page order desired.
+ * @order: max page order desired.
  * @errcode: pointer to error code if any
  * @gfp_mask: allocation mask
  *
@@ -6212,21 +6212,17 @@ EXPORT_SYMBOL_GPL(skb_mpls_dec_ttl);
  */
 struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
 				     unsigned long data_len,
-				     int max_page_order,
+				     int 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;
+	int nr_frags = 0;
 
 	*errcode = -EMSGSIZE;
-	/* Note this test could be relaxed, if we succeed to allocate
-	 * high order pages...
-	 */
-	if (npages > MAX_SKB_FRAGS)
+	if (unlikely(data_len > MAX_SKB_FRAGS * (PAGE_SIZE << order)))
 		return NULL;
 
 	*errcode = -ENOBUFS;
@@ -6234,34 +6230,32 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
 	if (!skb)
 		return NULL;
 
-	skb->truesize += npages << PAGE_SHIFT;
-
-	for (i = 0; npages > 0; i++) {
-		int order = max_page_order;
-
-		while (order) {
-			if (npages >= 1 << order) {
-				page = alloc_pages((gfp_mask & ~__GFP_DIRECT_RECLAIM) |
-						   __GFP_COMP |
-						   __GFP_NOWARN,
-						   order);
-				if (page)
-					goto fill_page;
-				/* Do not retry other high order allocations */
-				order = 1;
-				max_page_order = 0;
-			}
+	while (data_len) {
+		if (nr_frags == MAX_SKB_FRAGS - 1)
+			goto failure;
+		while (order && PAGE_ALIGN(data_len) < (PAGE_SIZE << order))
 			order--;
+
+		if (order) {
+			page = alloc_pages((gfp_mask & ~__GFP_DIRECT_RECLAIM) |
+					   __GFP_COMP |
+					   __GFP_NOWARN,
+					   order);
+			if (!page) {
+				order--;
+				continue;
+			}
+		} else {
+			page = alloc_page(gfp_mask);
+			if (!page)
+				goto failure;
 		}
-		page = alloc_page(gfp_mask);
-		if (!page)
-			goto failure;
-fill_page:
 		chunk = min_t(unsigned long, data_len,
 			      PAGE_SIZE << order);
-		skb_fill_page_desc(skb, i, page, 0, chunk);
+		skb_fill_page_desc(skb, nr_frags, page, 0, chunk);
+		nr_frags++;
+		skb->truesize += (PAGE_SIZE << order);
 		data_len -= chunk;
-		npages -= 1 << order;
 	}
 	return skb;