Subject: [RFC PATCH v2 11/21] core/skbuff: add page recycling logic for netgpu pages

From: Jonathan Lemon <[email-masked]>
Date: Mon, 27 Jul 2020 15:44:34 -0700

From: Jonathan Lemon <[email-masked]>

netgpu pages will always have a refcount of at least one (held by
the netgpu module).  If the skb is marked as containing netgpu ZC
pages, recycle them back to netgpu.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 net/core/skbuff.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1422b99b7090..50dbb7ce1965 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -591,6 +591,27 @@ static void skb_free_head(struct sk_buff *skb)
 		kfree(head);
 }
 
+#if IS_ENABLED(CONFIG_NETGPU)
+static void skb_netgpu_unref(struct skb_shared_info *shinfo)
+{
+	struct netgpu_ifq *ifq = shinfo->destructor_arg;
+	struct page *page;
+	int i;
+
+	/* pages attached for skbs for TX shouldn't come here, since
+	 * the skb is not marked as "zc_netgpu". (only RX skbs have this).
+	 * dummy page does come here, but always has elevated refc.
+	 *
+	 * Undelivered zc skb's will arrive at this point.
+	 */
+	for (i = 0; i < shinfo->nr_frags; i++) {
+		page = skb_frag_page(&shinfo->frags[i]);
+		if (page && page_ref_dec_return(page) <= 2)
+			netgpu_put_page(ifq, page, false);
+	}
+}
+#endif
+
 static void skb_release_data(struct sk_buff *skb)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
@@ -601,8 +622,15 @@ static void skb_release_data(struct sk_buff *skb)
 			      &shinfo->dataref))
 		return;
 
-	for (i = 0; i < shinfo->nr_frags; i++)
-		__skb_frag_unref(&shinfo->frags[i]);
+#if IS_ENABLED(CONFIG_NETGPU)
+	if (skb->zc_netgpu && shinfo->nr_frags) {
+		skb_netgpu_unref(shinfo);
+	} else
+#endif
+	{
+		for (i = 0; i < shinfo->nr_frags; i++)
+			__skb_frag_unref(&shinfo->frags[i]);
+	}
 
 	if (shinfo->frag_list)
 		kfree_skb_list(shinfo->frag_list);
-- 
2.24.1