net: mana: Reuse XDP dropped page

Reuse the dropped page in RX path to save page allocation
overhead.
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/microsoft/mana/mana.h

@@ -310,6 +310,7 @@ struct mana_rxq {
 
 	struct bpf_prog __rcu *bpf_prog;
 	struct xdp_rxq_info xdp_rxq;
+	struct page *xdp_save_page;
 
 	/* MUST BE THE LAST MEMBER:
 	 * Each receive buffer has an associated mana_recv_buf_oob.

drivers/net/ethernet/microsoft/mana/mana_en.c

@@ -1059,7 +1059,9 @@ static void mana_rx_skb(void *buf_va, struct mana_rxcomp_oob *cqe,
 	u64_stats_update_end(&rx_stats->syncp);
 
 drop:
-	free_page((unsigned long)buf_va);
+	WARN_ON_ONCE(rxq->xdp_save_page);
+	rxq->xdp_save_page = virt_to_page(buf_va);
+
 	++ndev->stats.rx_dropped;
 
 	return;
@@ -1116,7 +1118,13 @@ static void mana_process_rx_cqe(struct mana_rxq *rxq, struct mana_cq *cq,
 	rxbuf_oob = &rxq->rx_oobs[curr];
 	WARN_ON_ONCE(rxbuf_oob->wqe_inf.wqe_size_in_bu != 1);
 
-	new_page = alloc_page(GFP_ATOMIC);
+	/* Reuse XDP dropped page if available */
+	if (rxq->xdp_save_page) {
+		new_page = rxq->xdp_save_page;
+		rxq->xdp_save_page = NULL;
+	} else {
+		new_page = alloc_page(GFP_ATOMIC);
+	}
 
 	if (new_page) {
 		da = dma_map_page(dev, new_page, XDP_PACKET_HEADROOM, rxq->datasize,
@@ -1403,6 +1411,9 @@ static void mana_destroy_rxq(struct mana_port_context *apc,
 
 	mana_deinit_cq(apc, &rxq->rx_cq);
 
+	if (rxq->xdp_save_page)
+		__free_page(rxq->xdp_save_page);
+
 	for (i = 0; i < rxq->num_rx_buf; i++) {
 		rx_oob = &rxq->rx_oobs[i];