[PATCH net-next 2/2] tuntap: free XDP dropped packets in a batch

[Jason Wang]

Thanks to the batched XDP buffs through msg_control. Instead of
calling put_page() for each page which involves a atomic operation,
let's batch them by record the last page that needs to be freed and
its refcnt count and free them in a batch.

Testpmd(virtio-user + vhost_net) + XDP_DROP shows 3.8% improvement.

Before: 4.71Mpps
After : 4.89Mpps

Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 drivers/net/tun.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a65779c6d72f..e90a7923a5f6 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -188,6 +188,11 @@ struct tun_file {
        struct xdp_rxq_info xdp_rxq;
 };
 
+struct tun_page {
+       struct page *page;
+       int count;
+};
+
 struct tun_flow_entry {
        struct hlist_node hash_link;
        struct rcu_head rcu;
@@ -2377,9 +2382,16 @@ static void tun_sock_write_space(struct sock *sk)
        kill_fasync(&tfile->fasync, SIGIO, POLL_OUT);
 }
 
+static void tun_put_page(struct tun_page *tpage)
+{
+       if (tpage->page)
+               __page_frag_cache_drain(tpage->page, tpage->count);
+}
+
 static int tun_xdp_one(struct tun_struct *tun,
                       struct tun_file *tfile,
-                      struct xdp_buff *xdp, int *flush)
+                      struct xdp_buff *xdp, int *flush,
+                      struct tun_page *tpage)
 {
        struct tun_xdp_hdr *hdr = xdp->data_hard_start;
        struct virtio_net_hdr *gso = &hdr->gso;
@@ -2390,6 +2402,7 @@ static int tun_xdp_one(struct tun_struct *tun,
        int buflen = hdr->buflen;
        int err = 0;
        bool skb_xdp = false;
+       struct page *page;
 
        xdp_prog = rcu_dereference(tun->xdp_prog);
        if (xdp_prog) {
@@ -2416,7 +2429,14 @@ static int tun_xdp_one(struct tun_struct *tun,
                case XDP_PASS:
                        break;
                default:
-                       put_page(virt_to_head_page(xdp->data));
+                       page = virt_to_head_page(xdp->data);
+                       if (tpage->page == page) {
+                               ++tpage->count;
+                       } else {
+                               tun_put_page(tpage);
+                               tpage->page = page;
+                               tpage->count = 1;
+                       }
                        return 0;
                }
        }
@@ -2480,6 +2500,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr 
*m, size_t total_len)
                return -EBADFD;
 
        if (ctl && (ctl->type == TUN_MSG_PTR)) {
+               struct tun_page tpage = {0};
                int n = ctl->num;
                int flush = 0;
 
@@ -2488,7 +2509,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr 
*m, size_t total_len)
 
                for (i = 0; i < n; i++) {
                        xdp = &((struct xdp_buff *)ctl->ptr)[i];
-                       tun_xdp_one(tun, tfile, xdp, &flush);
+                       tun_xdp_one(tun, tfile, xdp, &flush, &tpage);
                }
 
                if (flush)
@@ -2497,6 +2518,8 @@ static int tun_sendmsg(struct socket *sock, struct msghdr 
*m, size_t total_len)
                rcu_read_unlock();
                local_bh_enable();
 
+               tun_put_page(&tpage);
+
                ret = total_len;
                goto out;
        }
-- 
2.17.1

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