[PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[Rusty Russell]

From: Mark McLoughlin <markmc@redhat.com>

Each time we re-fill the recv queue with buffers, we allocate
one too many skbs and free it again when adding fails. We should
recycle the pages allocated in this case.

A previous version of this patch made trim_pages() trim trailing
unused pages from skbs with some paged data, but this actually
caused a barely measurable slowdown.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv)
---
 drivers/net/virtio_net.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0196a0d..985271a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi, struct 
page *page)
 	vi->pages = page;
 }
 
+static void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
+{
+	unsigned int i;
+
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+		give_a_page(vi, skb_shinfo(skb)->frags[i].page);
+	skb_shinfo(skb)->nr_frags = 0;
+	skb->data_len = 0;
+}
+
 static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
 {
 	struct page *p = vi->pages;
@@ -121,14 +131,8 @@ static void receive_skb(struct net_device *dev, struct 
sk_buff *skb,
 	}
 	len -= sizeof(struct virtio_net_hdr);
 
-	if (len <= MAX_PACKET_LEN) {
-		unsigned int i;
-
-		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
-			give_a_page(dev->priv, skb_shinfo(skb)->frags[i].page);
-		skb->data_len = 0;
-		skb_shinfo(skb)->nr_frags = 0;
-	}
+	if (len <= MAX_PACKET_LEN)
+		trim_pages(netdev_priv(dev), skb);
 
 	err = pskb_trim(skb, len);
 	if (err) {
@@ -232,6 +236,7 @@ static void try_fill_recv(struct virtnet_info *vi)
 		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
 		if (err) {
 			skb_unlink(skb, &vi->recv);
+			trim_pages(vi, skb);
 			kfree_skb(skb);
 			break;
 		}
\0

[PATCH 2/3] virtio_net: hook up the set-tso ethtool op

[Rusty Russell]

From: Mark McLoughlin <markmc@redhat.com>

Seems like an oversight that we have set-tx-csum and set-sg hooked
up, but not set-tso.

Also leads to the strange situation that if you e.g. disable tx-csum,
then tso doesn't get disabled.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 drivers/net/virtio_net.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index cca6435..79b59cc 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -612,6 +612,7 @@ static int virtnet_set_tx_csum(struct net_device *dev, u32 data)
 static struct ethtool_ops virtnet_ethtool_ops = {
 	.set_tx_csum = virtnet_set_tx_csum,
 	.set_sg = ethtool_op_set_sg,
+	.set_tso = ethtool_op_set_tso,
 };
 
 static int virtnet_probe(struct virtio_device *vdev)

[PATCH 3/3] virtio_net: VIRTIO_NET_F_MSG_RXBUF (imprive rcv buffer allocation)

[Rusty Russell]

From: Mark McLoughlin <markmc@redhat.com>

If segmentation offload is enabled by the host, we currently allocate
maximum sized packet buffers and pass them to the host. This uses up
20 ring entries, allowing us to supply only 20 packet buffers to the
host with a 256 entry ring. This is a huge overhead when receiving
small packets, and is most keenly felt when receiving MTU sized
packets from off-host.

The VIRTIO_NET_F_MRG_RXBUF feature flag is set by hosts which support
using receive buffers which are smaller than the maximum packet size.
In order to transfer large packets to the guest, the host merges
together multiple receive buffers to form a larger logical buffer.
The number of merged buffers is returned to the guest via a field in
the virtio_net_hdr.

Make use of this support by supplying single page receive buffers to
the host. On receive, we extract the virtio_net_hdr, copy 128 bytes of
the payload to the skb's linear data buffer and adjust the fragment
offset to point to the remaining data. This ensures proper alignment
and allows us to not use any paged data for small packets. If the
payload occupies multiple pages, we simply append those pages as
fragments and free the associated skbs.

This scheme allows us to be efficient in our use of ring entries
while still supporting large packets. Benchmarking using netperf from
an external machine to a guest over a 10Gb/s network shows a 100%
improvement from ~1Gb/s to ~2Gb/s. With a local host->guest benchmark
with GSO disabled on the host side, throughput was seen to increase
from 700Mb/s to 1.7Gb/s.

Based on a patch from Herbert Xu.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv)
---
 drivers/net/virtio_net.c   |  173 +++++++++++++++++++++++++++++++++++++++------
 include/linux/virtio_net.h |    9 ++
 2 files changed, 162 insertions(+), 20 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -34,6 +34,7 @@ module_param(gso, bool, 0444);
 
 /* FIXME: MTU in config. */
 #define MAX_PACKET_LEN (ETH_HLEN+ETH_DATA_LEN)
+#define GOOD_COPY_LEN	128
 
 struct virtnet_info
 {
@@ -58,6 +59,9 @@ struct virtnet_info
 	/* I like... big packets and I cannot lie! */
 	bool big_packets;
 
+	/* Host will merge rx buffers for big packets (shake it! shake it!) */
+	bool mergeable_rx_bufs;
+
 	/* Receive & send queues. */
 	struct sk_buff_head recv;
 	struct sk_buff_head send;
@@ -66,14 +70,9 @@ struct virtnet_info
 	struct page *pages;
 };
 
-static inline struct virtio_net_hdr *skb_vnet_hdr(struct sk_buff *skb)
+static inline void *skb_vnet_hdr(struct sk_buff *skb)
 {
 	return (struct virtio_net_hdr *)skb->cb;
-}
-
-static inline void vnet_hdr_to_sg(struct scatterlist *sg, struct sk_buff *skb)
-{
-	sg_init_one(sg, skb_vnet_hdr(skb), sizeof(struct virtio_net_hdr));
 }
 
 static void give_a_page(struct virtnet_info *vi, struct page *page)
@@ -121,25 +120,97 @@ static void receive_skb(struct net_devic
 static void receive_skb(struct net_device *dev, struct sk_buff *skb,
 			unsigned len)
 {
+	struct virtnet_info *vi = netdev_priv(dev);
 	struct virtio_net_hdr *hdr = skb_vnet_hdr(skb);
 	int err;
+	int i;
 
 	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
 		pr_debug("%s: short packet %i\n", dev->name, len);
 		dev->stats.rx_length_errors++;
 		goto drop;
 	}
-	len -= sizeof(struct virtio_net_hdr);
 
-	if (len <= MAX_PACKET_LEN)
-		trim_pages(netdev_priv(dev), skb);
+	if (vi->mergeable_rx_bufs) {
+		struct virtio_net_hdr_mrg_rxbuf *mhdr = skb_vnet_hdr(skb);
+		unsigned int copy;
+		char *p = page_address(skb_shinfo(skb)->frags[0].page);
 
-	err = pskb_trim(skb, len);
-	if (err) {
-		pr_debug("%s: pskb_trim failed %i %d\n", dev->name, len, err);
-		dev->stats.rx_dropped++;
-		goto drop;
+		if (len > PAGE_SIZE)
+			len = PAGE_SIZE;
+		len -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
+
+		memcpy(hdr, p, sizeof(*mhdr));
+		p += sizeof(*mhdr);
+
+		copy = len;
+		if (copy > skb_tailroom(skb))
+			copy = skb_tailroom(skb);
+
+		memcpy(skb_put(skb, copy), p, copy);
+
+		len -= copy;
+
+		if (!len) {
+			give_a_page(vi, skb_shinfo(skb)->frags[0].page);
+			skb_shinfo(skb)->nr_frags--;
+		} else {
+			skb_shinfo(skb)->frags[0].page_offset +=
+				sizeof(*mhdr) + copy;
+			skb_shinfo(skb)->frags[0].size = len;
+			skb->data_len += len;
+			skb->len += len;
+		}
+
+		while (--mhdr->num_buffers) {
+			struct sk_buff *nskb;
+
+			i = skb_shinfo(skb)->nr_frags;
+			if (i >= MAX_SKB_FRAGS) {
+				pr_debug("%s: packet too long %d\n", dev->name,
+					 len);
+				dev->stats.rx_length_errors++;
+				goto drop;
+			}
+
+			nskb = vi->rvq->vq_ops->get_buf(vi->rvq, &len);
+			if (!nskb) {
+				pr_debug("%s: rx error: %d buffers missing\n",
+					 dev->name, mhdr->num_buffers);
+				dev->stats.rx_length_errors++;
+				goto drop;
+			}
+
+			__skb_unlink(nskb, &vi->recv);
+			vi->num--;
+
+			skb_shinfo(skb)->frags[i] = skb_shinfo(nskb)->frags[0];
+			skb_shinfo(nskb)->nr_frags = 0;
+			kfree_skb(nskb);
+
+			if (len > PAGE_SIZE)
+				len = PAGE_SIZE;
+
+			skb_shinfo(skb)->frags[i].size = len;
+			skb_shinfo(skb)->nr_frags++;
+			skb->data_len += len;
+			skb->len += len;
+		}
+	} else {
+		len -= sizeof(struct virtio_net_hdr);
+
+		if (len <= MAX_PACKET_LEN)
+			trim_pages(vi, skb);
+
+		err = pskb_trim(skb, len);
+		if (err) {
+			pr_debug("%s: pskb_trim failed %i %d\n", dev->name,
+				 len, err);
+			dev->stats.rx_dropped++;
+			goto drop;
+		}
 	}
+
 	skb->truesize += skb->data_len;
 	dev->stats.rx_bytes += skb->len;
 	dev->stats.rx_packets++;
@@ -198,7 +269,7 @@ drop:
 	dev_kfree_skb(skb);
 }
 
-static void try_fill_recv(struct virtnet_info *vi)
+static void try_fill_recv_maxbufs(struct virtnet_info *vi)
 {
 	struct sk_buff *skb;
 	struct scatterlist sg[2+MAX_SKB_FRAGS];
@@ -206,12 +277,16 @@ static void try_fill_recv(struct virtnet
 
 	sg_init_table(sg, 2+MAX_SKB_FRAGS);
 	for (;;) {
+		struct virtio_net_hdr *hdr;
+
 		skb = netdev_alloc_skb(vi->dev, MAX_PACKET_LEN);
 		if (unlikely(!skb))
 			break;
 
 		skb_put(skb, MAX_PACKET_LEN);
-		vnet_hdr_to_sg(sg, skb);
+
+		hdr = skb_vnet_hdr(skb);
+		sg_init_one(sg, hdr, sizeof(*hdr));
 
 		if (vi->big_packets) {
 			for (i = 0; i < MAX_SKB_FRAGS; i++) {
@@ -237,6 +312,54 @@ static void try_fill_recv(struct virtnet
 		if (err) {
 			skb_unlink(skb, &vi->recv);
 			trim_pages(vi, skb);
+			kfree_skb(skb);
+			break;
+		}
+		vi->num++;
+	}
+	if (unlikely(vi->num > vi->max))
+		vi->max = vi->num;
+	vi->rvq->vq_ops->kick(vi->rvq);
+}
+
+static void try_fill_recv(struct virtnet_info *vi)
+{
+	struct sk_buff *skb;
+	struct scatterlist sg[1];
+	int err;
+
+	if (!vi->mergeable_rx_bufs) {
+		try_fill_recv_maxbufs(vi);
+		return;
+	}
+
+	for (;;) {
+		skb_frag_t *f;
+
+		skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
+		if (unlikely(!skb))
+			break;
+
+		skb_reserve(skb, NET_IP_ALIGN);
+
+		f = &skb_shinfo(skb)->frags[0];
+		f->page = get_a_page(vi, GFP_ATOMIC);
+		if (!f->page) {
+			kfree_skb(skb);
+			break;
+		}
+
+		f->page_offset = 0;
+		f->size = PAGE_SIZE;
+
+		skb_shinfo(skb)->nr_frags++;
+
+		sg_init_one(sg, page_address(f->page), PAGE_SIZE);
+		skb_queue_head(&vi->recv, skb);
+
+		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
+		if (err) {
+			skb_unlink(skb, &vi->recv);
 			kfree_skb(skb);
 			break;
 		}
@@ -325,7 +448,8 @@ static int xmit_skb(struct virtnet_info 
 {
 	int num, err;
 	struct scatterlist sg[2+MAX_SKB_FRAGS];
-	struct virtio_net_hdr *hdr;
+	struct virtio_net_hdr_mrg_rxbuf *mhdr = skb_vnet_hdr(skb);
+	struct virtio_net_hdr *hdr = skb_vnet_hdr(skb);
 	const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
 
 	sg_init_table(sg, 2+MAX_SKB_FRAGS);
@@ -334,8 +458,6 @@ static int xmit_skb(struct virtnet_info 
 		 dest[0], dest[1], dest[2],
 		 dest[3], dest[4], dest[5]);
 
-	/* Encode metadata header at front. */
-	hdr = skb_vnet_hdr(skb);
 	if (skb->ip_summed == CHECKSUM_PARTIAL) {
 		hdr->flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
 		hdr->csum_start = skb->csum_start - skb_headroom(skb);
@@ -363,7 +485,14 @@ static int xmit_skb(struct virtnet_info 
 		hdr->gso_size = hdr->hdr_len = 0;
 	}
 
-	vnet_hdr_to_sg(sg, skb);
+	mhdr->num_buffers = 0;
+
+	/* Encode metadata header at front. */
+	if (vi->mergeable_rx_bufs)
+		sg_init_one(sg, mhdr, sizeof(*mhdr));
+	else
+		sg_init_one(sg, hdr, sizeof(*hdr));
+
 	num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
 
 	err = vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
@@ -552,6 +681,9 @@ static int virtnet_probe(struct virtio_d
 	    || virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN))
 		vi->big_packets = true;
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
+		vi->mergeable_rx_bufs = true;
+
 	/* We expect two virtqueues, receive then send. */
 	vi->rvq = vdev->config->find_vq(vdev, 0, skb_recv_done);
 	if (IS_ERR(vi->rvq)) {
@@ -644,6 +776,7 @@ static unsigned int features[] = {
 	VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_UFO, VIRTIO_NET_F_HOST_TSO6,
 	VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
 	VIRTIO_NET_F_GUEST_ECN, /* We don't yet handle UFO input. */
+	VIRTIO_NET_F_MRG_RXBUF,
 	VIRTIO_F_NOTIFY_ON_EMPTY,
 };
 
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -20,6 +20,7 @@
 #define VIRTIO_NET_F_HOST_TSO6	12	/* Host can handle TSOv6 in. */
 #define VIRTIO_NET_F_HOST_ECN	13	/* Host can handle TSO[6] w/ ECN in. */
 #define VIRTIO_NET_F_HOST_UFO	14	/* Host can handle UFO in. */
+#define VIRTIO_NET_F_MRG_RXBUF	15	/* Host can merge receive buffers. */
 
 struct virtio_net_config
 {
@@ -44,4 +45,12 @@ struct virtio_net_hdr
 	__u16 csum_start;	/* Position to start checksumming from */
 	__u16 csum_offset;	/* Offset after that to place checksum */
 };
+
+/* This is the version of the header to use when the MRG_RXBUF
+ * feature has been negotiated. */
+struct virtio_net_hdr_mrg_rxbuf {
+	struct virtio_net_hdr hdr;
+	__u16 num_buffers;	/* Number of merged rx buffers */
+};
+
 #endif /* _LINUX_VIRTIO_NET_H */

Re: [PATCH 3/3] virtio_net: VIRTIO_NET_F_MSG_RXBUF (imprive rcv buffer allocation)

[David Miller]

From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 17 Nov 2008 13:47:42 +1030

> If segmentation offload is enabled by the host, we currently allocate
> maximum sized packet buffers and pass them to the host. This uses up
> 20 ring entries, allowing us to supply only 20 packet buffers to the
> host with a 256 entry ring. This is a huge overhead when receiving
> small packets, and is most keenly felt when receiving MTU sized
> packets from off-host.
> 
> The VIRTIO_NET_F_MRG_RXBUF feature flag is set by hosts which support
> using receive buffers which are smaller than the maximum packet size.
> In order to transfer large packets to the guest, the host merges
> together multiple receive buffers to form a larger logical buffer.
> The number of merged buffers is returned to the guest via a field in
> the virtio_net_hdr.
> 
> Make use of this support by supplying single page receive buffers to
> the host. On receive, we extract the virtio_net_hdr, copy 128 bytes of
> the payload to the skb's linear data buffer and adjust the fragment
> offset to point to the remaining data. This ensures proper alignment
> and allows us to not use any paged data for small packets. If the
> payload occupies multiple pages, we simply append those pages as
> fragments and free the associated skbs.
> 
> This scheme allows us to be efficient in our use of ring entries
> while still supporting large packets. Benchmarking using netperf from
> an external machine to a guest over a 10Gb/s network shows a 100%
> improvement from ~1Gb/s to ~2Gb/s. With a local host->guest benchmark
> with GSO disabled on the host side, throughput was seen to increase
> from 700Mb/s to 1.7Gb/s.
> 
> Based on a patch from Herbert Xu.
> 
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv)

Applied, but a lot of fuzz and differences when adding to net-next-2.6

Re: [PATCH 2/3] virtio_net: hook up the set-tso ethtool op

[David Miller]

From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 17 Nov 2008 13:46:08 +1030

> Seems like an oversight that we have set-tx-csum and set-sg hooked
> up, but not set-tso.
> 
> Also leads to the strange situation that if you e.g. disable tx-csum,
> then tso doesn't get disabled.
> 
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Applied.

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[David Miller]

From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 17 Nov 2008 13:44:57 +1030

> @@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi, struct 
> page *page)

-E_EMAIL_CLIENT_NEWLINES

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Sun, 16 Nov 2008 19:45:05 -0800 (PST)

> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Mon, 17 Nov 2008 13:44:57 +1030
> 
> > @@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi, struct 
> > page *page)
> 
> -E_EMAIL_CLIENT_NEWLINES

I got tired of sitting on my thumbs and waiting for the fixed version
of the patch, so I cleared it all out myself and added it to net-next-2.6

Even with the mail client corruption fix this thing didn't even apply
to net-next-2.6 :-(

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[Rusty Russell]

On Monday 17 November 2008 17:10:07 David Miller wrote:
> Even with the mail client corruption fix this thing didn't even apply
> to net-next-2.6 :-(

Assume this is the netdev_priv changes.  I'll drop my versions from linux-next 
to avoid screwing Stephen over.

Thanks,
Rusty.

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[David Miller]

From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 17 Nov 2008 17:38:54 +1030

> On Monday 17 November 2008 17:10:07 David Miller wrote:
> > Even with the mail client corruption fix this thing didn't even apply
> > to net-next-2.6 :-(
> 
> Assume this is the netdev_priv changes.  I'll drop my versions from linux-next 
> to avoid screwing Stephen over.

That's, that was the main point of this :-)

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[Rusty Russell]

On Monday 17 November 2008 14:15:05 David Miller wrote:
> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Mon, 17 Nov 2008 13:44:57 +1030
>
> > @@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi,
> > struct page *page)
>
> -E_EMAIL_CLIENT_NEWLINES

From: Mark McLoughlin <markmc@redhat.com>

Each time we re-fill the recv queue with buffers, we allocate
one too many skbs and free it again when adding fails. We should
recycle the pages allocated in this case.

A previous version of this patch made trim_pages() trim trailing
unused pages from skbs with some paged data, but this actually
caused a barely measurable slowdown.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv)
---
 drivers/net/virtio_net.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0196a0d..985271a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi, struct page *page)
 	vi->pages = page;
 }
 
+static void trim_pages(struct virtnet_info *vi, struct sk_buff *skb)
+{
+	unsigned int i;
+
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+		give_a_page(vi, skb_shinfo(skb)->frags[i].page);
+	skb_shinfo(skb)->nr_frags = 0;
+	skb->data_len = 0;
+}
+
 static struct page *get_a_page(struct virtnet_info *vi, gfp_t gfp_mask)
 {
 	struct page *p = vi->pages;
@@ -121,14 +131,8 @@ static void receive_skb(struct net_device *dev, struct sk_buff *skb,
 	}
 	len -= sizeof(struct virtio_net_hdr);
 
-	if (len <= MAX_PACKET_LEN) {
-		unsigned int i;
-
-		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
-			give_a_page(dev->priv, skb_shinfo(skb)->frags[i].page);
-		skb->data_len = 0;
-		skb_shinfo(skb)->nr_frags = 0;
-	}
+	if (len <= MAX_PACKET_LEN)
+		trim_pages(netdev_priv(dev), skb);
 
 	err = pskb_trim(skb, len);
 	if (err) {
@@ -232,6 +236,7 @@ static void try_fill_recv(struct virtnet_info *vi)
 		err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
 		if (err) {
 			skb_unlink(skb, &vi->recv);
+			trim_pages(vi, skb);
 			kfree_skb(skb);
 			break;
 		}

Re: [PATCH 1/3] virtio_net: Recycle some more rx buffer pages

[David Miller]

From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 17 Nov 2008 17:35:43 +1030

> On Monday 17 November 2008 14:15:05 David Miller wrote:
> > From: Rusty Russell <rusty@rustcorp.com.au>
> > Date: Mon, 17 Nov 2008 13:44:57 +1030
> >
> > > @@ -82,6 +82,16 @@ static void give_a_page(struct virtnet_info *vi,
> > > struct page *page)
> >
> > -E_EMAIL_CLIENT_NEWLINES
> 
> Each time we re-fill the recv queue with buffers, we allocate
> one too many skbs and free it again when adding fails. We should
> recycle the pages allocated in this case.
> 
> A previous version of this patch made trim_pages() trim trailing
> unused pages from skbs with some paged data, but this actually
> caused a barely measurable slowdown.
> 
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (use netdev_priv)

-ETOOLATE, and...

> -			give_a_page(dev->priv, skb_shinfo(skb)->frags[i].page);

this wouldn't have applied to net-next-2.6, the dev->priv reads
netdev_priv(dev) there.

Anyways, as I said in my other reply I fixed all of this up because
I was tired of waiting... :)