f_phonet: use page-sized rather than MTU-sized RX buffers

Instead of a large (physically) linear buffer, we generate a set of
paged sk_buff, so no extra memory copy is involved. This removes
high-order allocations and saves quite a bit of memory. Phonet MTU is
65541 bytes, so the two buffers were padded to 128 kilo-bytes each.
Now, we create 17 page buffers, almost a 75% memory use reduction.

Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/usb/gadget/f_phonet.c

@@ -35,6 +35,10 @@
 #include "u_phonet.h"
 
 #define PN_MEDIA_USB	0x1B
+#define MAXPACKET	512
+#if (PAGE_SIZE % MAXPACKET)
+#error MAXPACKET must divide PAGE_SIZE!
+#endif
 
 /*-------------------------------------------------------------------------*/
 
@@ -45,6 +49,10 @@ struct phonet_port {
 
 struct f_phonet {
 	struct usb_function		function;
+	struct {
+		struct sk_buff		*skb;
+		spinlock_t		lock;
+	} rx;
 	struct net_device		*dev;
 	struct usb_ep			*in_ep, *out_ep;
 
@@ -52,7 +60,7 @@ struct f_phonet {
 	struct usb_request		*out_reqv[0];
 };
 
-static int phonet_rxq_size = 2;
+static int phonet_rxq_size = 17;
 
 static inline struct f_phonet *func_to_pn(struct usb_function *f)
 {
@@ -138,7 +146,7 @@ pn_hs_sink_desc = {
 
 	.bEndpointAddress =	USB_DIR_OUT,
 	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
-	.wMaxPacketSize =	cpu_to_le16(512),
+	.wMaxPacketSize =	cpu_to_le16(MAXPACKET),
 };
 
 static struct usb_endpoint_descriptor
@@ -298,21 +306,21 @@ static void pn_net_setup(struct net_device *dev)
 static int
 pn_rx_submit(struct f_phonet *fp, struct usb_request *req, gfp_t gfp_flags)
 {
-	struct sk_buff *skb;
-	const size_t size = fp->dev->mtu;
+	struct net_device *dev = fp->dev;
+	struct page *page;
 	int err;
 
-	skb = alloc_skb(size, gfp_flags);
-	if (!skb)
+	page = __netdev_alloc_page(dev, gfp_flags);
+	if (!page)
 		return -ENOMEM;
 
-	req->buf = skb->data;
-	req->length = size;
-	req->context = skb;
+	req->buf = page_address(page);
+	req->length = PAGE_SIZE;
+	req->context = page;
 
 	err = usb_ep_queue(fp->out_ep, req, gfp_flags);
 	if (unlikely(err))
-		dev_kfree_skb_any(skb);
+		netdev_free_page(dev, page);
 	return err;
 }
 
@@ -320,25 +328,37 @@ static void pn_rx_complete(struct usb_ep *ep, struct usb_request *req)
 {
 	struct f_phonet *fp = ep->driver_data;
 	struct net_device *dev = fp->dev;
-	struct sk_buff *skb = req->context;
+	struct page *page = req->context;
+	struct sk_buff *skb;
+	unsigned long flags;
 	int status = req->status;
 
 	switch (status) {
 	case 0:
-		if (unlikely(!netif_running(dev)))
-			break;
-		if (unlikely(req->actual < 1))
+		spin_lock_irqsave(&fp->rx.lock, flags);
+		skb = fp->rx.skb;
+		if (!skb)
+			skb = fp->rx.skb = netdev_alloc_skb(dev, 12);
+		if (req->actual < req->length) /* Last fragment */
+			fp->rx.skb = NULL;
+		spin_unlock_irqrestore(&fp->rx.lock, flags);
+
+		if (unlikely(!skb))
 			break;
-		skb_put(skb, req->actual);
-		skb->protocol = htons(ETH_P_PHONET);
-		skb_reset_mac_header(skb);
-		__skb_pull(skb, 1);
-		skb->dev = dev;
-		dev->stats.rx_packets++;
-		dev->stats.rx_bytes += skb->len;
-
-		netif_rx(skb);
-		skb = NULL;
+		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, 0,
+				req->actual);
+		page = NULL;
+
+		if (req->actual < req->length) { /* Last fragment */
+			skb->protocol = htons(ETH_P_PHONET);
+			skb_reset_mac_header(skb);
+			pskb_pull(skb, 1);
+			skb->dev = dev;
+			dev->stats.rx_packets++;
+			dev->stats.rx_bytes += skb->len;
+
+			netif_rx(skb);
+		}
 		break;
 
 	/* Do not resubmit in these cases: */
@@ -356,8 +376,8 @@ static void pn_rx_complete(struct usb_ep *ep, struct usb_request *req)
 		break;
 	}
 
-	if (skb)
-		dev_kfree_skb_any(skb);
+	if (page)
+		netdev_free_page(dev, page);
 	if (req)
 		pn_rx_submit(fp, req, GFP_ATOMIC);
 }
@@ -375,6 +395,10 @@ static void __pn_reset(struct usb_function *f)
 
 	usb_ep_disable(fp->out_ep);
 	usb_ep_disable(fp->in_ep);
+	if (fp->rx.skb) {
+		dev_kfree_skb_irq(fp->rx.skb);
+		fp->rx.skb = NULL;
+	}
 }
 
 static int pn_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
@@ -573,6 +597,7 @@ int __init phonet_bind_config(struct usb_configuration *c)
 	fp->function.set_alt = pn_set_alt;
 	fp->function.get_alt = pn_get_alt;
 	fp->function.disable = pn_disconnect;
+	spin_lock_init(&fp->rx.lock);
 
 	err = usb_add_function(c, &fp->function);
 	if (err)