[RFC PATCH 19/21] core: add page recycling logic for netgpu pages

[Jonathan Lemon <jonathan.lemon@gmail.com>]

netgpu pages will always have a refcount of at least one (held by
the netgpu module).  This logic and the codepath obviously needs
work, but suffices for a proof-of-concept.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
---
 net/core/skbuff.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2a391042be53..2b4176cab578 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -69,6 +69,7 @@
 #include <net/xfrm.h>
 #include <net/mpls.h>
 #include <net/mptcp.h>
+#include <net/netgpu.h>
 
 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
@@ -590,6 +591,24 @@ static void skb_free_head(struct sk_buff *skb)
 		kfree(head);
 }
 
+static void skb_netgpu_unref(struct skb_shared_info *shinfo)
+{
+	struct page *page;
+	int count;
+	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.
+	 */
+	for (i = 0; i < shinfo->nr_frags; i++) {
+		page = skb_frag_page(&shinfo->frags[i]);
+		count = page_ref_dec_return(page);
+		if (count <= 2)
+			__netgpu_put_page(g_ctx, page, false);
+	}
+}
+
 static void skb_release_data(struct sk_buff *skb)
 {
 	struct skb_shared_info *shinfo = skb_shinfo(skb);
@@ -600,8 +619,12 @@ 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 (skb->zc_netgpu && shinfo->nr_frags) {
+		skb_netgpu_unref(shinfo);
+	} else {
+		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