netdev - [PATCH ipsec-next v3 10/17] xfrm: iptfs: share page fragments of inner packets

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Date: Fri,  7 Jun 2024 01:40:34 -0400
From: Christian Hopps <chopps@...pps.org>
To: devel@...ux-ipsec.org
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
	netdev@...r.kernel.org,
	Christian Hopps <chopps@...pps.org>,
	Christian Hopps <chopps@...n.net>
Subject: [PATCH ipsec-next v3 10/17] xfrm: iptfs: share page fragments of inner packets

From: Christian Hopps <chopps@...n.net>

When possible rather than appending secondary (aggregated) inner packets
to the fragment list, share their page fragments with the outer IPTFS
packet. This allows for more efficient packet transmission.

Signed-off-by: Christian Hopps <chopps@...n.net>
---
 net/xfrm/xfrm_iptfs.c | 88 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 79 insertions(+), 9 deletions(-)

diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
index 8911f9e50a30..200945f7ed40 100644
--- a/net/xfrm/xfrm_iptfs.c
+++ b/net/xfrm/xfrm_iptfs.c
@@ -45,6 +45,24 @@ struct xfrm_iptfs_data {
 static u32 iptfs_get_inner_mtu(struct xfrm_state *x, int outer_mtu);
 static enum hrtimer_restart iptfs_delay_timer(struct hrtimer *me);
 
+/* ================= */
+/* SK_BUFF Functions */
+/* ================= */
+
+/**
+ * skb_head_to_frag() - initialize a skb_frag_t based on skb head data
+ * @skb: skb with the head data
+ * @frag: frag to initialize
+ */
+static void skb_head_to_frag(const struct sk_buff *skb, skb_frag_t *frag)
+{
+	struct page *page = virt_to_head_page(skb->data);
+	unsigned char *addr = (unsigned char *)page_address(page);
+
+	BUG_ON(!skb->head_frag);
+	skb_frag_fill_page_desc(frag, page, skb->data - addr, skb_headlen(skb));
+}
+
 /* ================================= */
 /* IPTFS Sending (ingress) Functions */
 /* ================================= */
@@ -262,14 +280,44 @@ static struct sk_buff **iptfs_rehome_fraglist(struct sk_buff **nextp,
 	return nextp;
 }
 
+static void iptfs_consume_frags(struct sk_buff *to, struct sk_buff *from)
+{
+	struct skb_shared_info *fromi = skb_shinfo(from);
+	struct skb_shared_info *toi = skb_shinfo(to);
+	unsigned int new_truesize;
+
+	/* If we have data in a head page, grab it */
+	if (!skb_headlen(from)) {
+		new_truesize = SKB_TRUESIZE(skb_end_offset(from));
+	} else {
+		skb_head_to_frag(from, &toi->frags[toi->nr_frags]);
+		skb_frag_ref(to, toi->nr_frags++);
+		new_truesize = SKB_DATA_ALIGN(sizeof(struct sk_buff));
+	}
+
+	/* Move any other page fragments rather than copy */
+	memcpy(&toi->frags[toi->nr_frags], fromi->frags,
+	       sizeof(fromi->frags[0]) * fromi->nr_frags);
+	toi->nr_frags += fromi->nr_frags;
+	fromi->nr_frags = 0;
+	from->data_len = 0;
+	from->len = 0;
+	to->truesize += from->truesize - new_truesize;
+	from->truesize = new_truesize;
+
+	/* We are done with this SKB */
+	consume_skb(from);
+}
+
 static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
 {
 	struct xfrm_iptfs_data *xtfs = x->mode_data;
 	struct sk_buff *skb, *skb2, **nextp;
-	struct skb_shared_info *shi;
+	struct skb_shared_info *shi, *shi2;
 
 	while ((skb = __skb_dequeue(list))) {
 		u32 mtu = iptfs_get_cur_pmtu(x, xtfs, skb);
+		bool share_ok = true;
 		int remaining;
 
 		/* protocol comes to us cleared sometimes */
@@ -314,7 +362,7 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
 
 		/* Re-home (un-nest) nested fragment lists. We need to do this
 		 * b/c we will simply be appending any following aggregated
-		 * inner packets to the frag list.
+		 * inner packets using the frag list.
 		 */
 		shi = skb_shinfo(skb);
 		nextp = &shi->frag_list;
@@ -326,6 +374,9 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
 				nextp = &(*nextp)->next;
 		}
 
+		if (shi->frag_list || skb_cloned(skb) || skb_shared(skb))
+			share_ok = false;
+
 		/* See if we have enough space to simply append.
 		 *
 		 * NOTE: Maybe do not append if we will be mis-aligned,
@@ -351,18 +402,37 @@ static void iptfs_output_queued(struct xfrm_state *x, struct sk_buff_head *list)
 				}
 			}
 
+			/* skb->pp_recycle is passed to __skb_flag_unref for all
+			 * frag pages so we can only share pages with skb's who
+			 * match ourselves.
+			 */
+			shi2 = skb_shinfo(skb2);
+			if (share_ok &&
+			    (shi2->frag_list ||
+			     (!skb2->head_frag && skb_headlen(skb)) ||
+			     skb->pp_recycle != skb2->pp_recycle ||
+			     skb_zcopy(skb2) ||
+			     (shi->nr_frags + shi2->nr_frags + 1 >
+			      MAX_SKB_FRAGS)))
+				share_ok = false;
+
 			/* Do accounting */
 			skb->data_len += skb2->len;
 			skb->len += skb2->len;
 			remaining -= skb2->len;
 
-			/* Append to the frag_list */
-			*nextp = skb2;
-			nextp = &skb2->next;
-			BUG_ON(*nextp);
-			if (skb_has_frag_list(skb2))
-				nextp = iptfs_rehome_fraglist(nextp, skb2);
-			skb->truesize += skb2->truesize;
+			if (share_ok) {
+				iptfs_consume_frags(skb, skb2);
+			} else {
+				/* Append to the frag_list */
+				*nextp = skb2;
+				nextp = &skb2->next;
+				BUG_ON(*nextp);
+				if (skb_has_frag_list(skb2))
+					nextp = iptfs_rehome_fraglist(nextp,
+								      skb2);
+				skb->truesize += skb2->truesize;
+			}
 		}
 
 		xfrm_output(NULL, skb);
-- 
2.45.2