Linux Virtualization - Oct 2013 - [PATCH net-next] virtio_net: migrate mergeable rx buffers to page frag allocators

The virtio_net driver's mergeable receive buffer allocator
uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
is > 4KB but only ~1500 bytes of the buffer is used to store
packet data, reducing the effective TCP window size
substantially. This patch addresses the performance concerns
with mergeable receive buffers by allocating MTU-sized packet
buffers using page frag allocators. If more than MAX_SKB_FRAGS
buffers are needed, the SKB frag_list is used.

Signed-off-by: Michael Dalton <mwdalton at google.com>
---
 drivers/net/virtio_net.c | 164 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 106 insertions(+), 58 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9fbdfcd..113ee93 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -124,6 +124,11 @@ struct virtnet_info {
 	/* Lock for config space updates */
 	struct mutex config_lock;
 
+	/* Page_frag for GFP_KERNEL packet buffer allocation when we run
+	 * low on memory.
+	 */
+	struct page_frag alloc_frag;
+
 	/* Does the affinity hint is set for virtqueues? */
 	bool affinity_hint_set;
 
@@ -217,33 +222,18 @@ static void skb_xmit_done(struct virtqueue *vq)
 	netif_wake_subqueue(vi->dev, vq2txq(vq));
 }
 
-static void set_skb_frag(struct sk_buff *skb, struct page *page,
-			 unsigned int offset, unsigned int *len)
-{
-	int size = min((unsigned)PAGE_SIZE - offset, *len);
-	int i = skb_shinfo(skb)->nr_frags;
-
-	__skb_fill_page_desc(skb, i, page, offset, size);
-
-	skb->data_len += size;
-	skb->len += size;
-	skb->truesize += PAGE_SIZE;
-	skb_shinfo(skb)->nr_frags++;
-	skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
-	*len -= size;
-}
-
 /* Called from bottom half context */
 static struct sk_buff *page_to_skb(struct receive_queue *rq,
-				   struct page *page, unsigned int len)
+				   struct page *page, unsigned int offset,
+				   unsigned int len, unsigned int truesize)
 {
 	struct virtnet_info *vi = rq->vq->vdev->priv;
 	struct sk_buff *skb;
 	struct skb_vnet_hdr *hdr;
-	unsigned int copy, hdr_len, offset;
+	unsigned int copy, hdr_len, hdr_padded_len;
 	char *p;
 
-	p = page_address(page);
+	p = page_address(page) + offset;
 
 	/* copy small packet so we can reuse these pages for small data */
 	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
@@ -254,16 +244,17 @@ static struct sk_buff *page_to_skb(struct receive_queue
*rq,
 
 	if (vi->mergeable_rx_bufs) {
 		hdr_len = sizeof hdr->mhdr;
-		offset = hdr_len;
+		hdr_padded_len = sizeof hdr->mhdr;
 	} else {
 		hdr_len = sizeof hdr->hdr;
-		offset = sizeof(struct padded_vnet_hdr);
+		hdr_padded_len = sizeof(struct padded_vnet_hdr);
 	}
 
 	memcpy(hdr, p, hdr_len);
 
 	len -= hdr_len;
-	p += offset;
+	offset += hdr_padded_len;
+	p += hdr_padded_len;
 
 	copy = len;
 	if (copy > skb_tailroom(skb))
@@ -273,6 +264,14 @@ static struct sk_buff *page_to_skb(struct receive_queue
*rq,
 	len -= copy;
 	offset += copy;
 
+	if (vi->mergeable_rx_bufs) {
+		if (len)
+			skb_add_rx_frag(skb, 0, page, offset, len, truesize);
+		else
+			put_page(page);
+		return skb;
+	}
+
 	/*
 	 * Verify that we can indeed put this data into a skb.
 	 * This is here to handle cases when the device erroneously
@@ -284,9 +283,12 @@ static struct sk_buff *page_to_skb(struct receive_queue
*rq,
 		dev_kfree_skb(skb);
 		return NULL;
 	}
-
+	BUG_ON(offset >= PAGE_SIZE);
 	while (len) {
-		set_skb_frag(skb, page, offset, &len);
+		unsigned int frag_size = min((unsigned)PAGE_SIZE - offset, len);
+		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset,
+				frag_size, truesize);
+		len -= frag_size;
 		page = (struct page *)page->private;
 		offset = 0;
 	}
@@ -297,33 +299,52 @@ static struct sk_buff *page_to_skb(struct receive_queue
*rq,
 	return skb;
 }
 
-static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
+static int receive_mergeable(struct receive_queue *rq, struct sk_buff
*head_skb)
 {
-	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
+	struct skb_vnet_hdr *hdr = skb_vnet_hdr(head_skb);
+	struct sk_buff *curr_skb = head_skb;
+	char *buf;
 	struct page *page;
-	int num_buf, i, len;
+	int num_buf, len;
 
 	num_buf = hdr->mhdr.num_buffers;
 	while (--num_buf) {
-		i = skb_shinfo(skb)->nr_frags;
-		if (i >= MAX_SKB_FRAGS) {
-			pr_debug("%s: packet too long\n", skb->dev->name);
-			skb->dev->stats.rx_length_errors++;
-			return -EINVAL;
-		}
-		page = virtqueue_get_buf(rq->vq, &len);
-		if (!page) {
+		int num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
+		buf = virtqueue_get_buf(rq->vq, &len);
+		if (unlikely(!buf)) {
 			pr_debug("%s: rx error: %d buffers missing\n",
-				 skb->dev->name, hdr->mhdr.num_buffers);
-			skb->dev->stats.rx_length_errors++;
+				 head_skb->dev->name, hdr->mhdr.num_buffers);
+			head_skb->dev->stats.rx_length_errors++;
 			return -EINVAL;
 		}
-
-		if (len > PAGE_SIZE)
-			len = PAGE_SIZE;
-
-		set_skb_frag(skb, page, 0, &len);
-
+		if (unlikely(len > MAX_PACKET_LEN)) {
+			pr_debug("%s: rx error: merge buffer too long\n",
+				 head_skb->dev->name);
+			len = MAX_PACKET_LEN;
+		}
+		if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
+			struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
+			if (unlikely(!nskb)) {
+				head_skb->dev->stats.rx_dropped++;
+				return -ENOMEM;
+			}
+			if (curr_skb == head_skb)
+				skb_shinfo(curr_skb)->frag_list = nskb;
+			else
+				curr_skb->next = nskb;
+			curr_skb = nskb;
+			head_skb->truesize += nskb->truesize;
+			num_skb_frags = 0;
+		}
+		if (curr_skb != head_skb) {
+			head_skb->data_len += len;
+			head_skb->len += len;
+			head_skb->truesize += MAX_PACKET_LEN;
+		}
+		page = virt_to_head_page(buf);
+		skb_add_rx_frag(curr_skb, num_skb_frags, page,
+				buf - (char *)page_address(page), len,
+				MAX_PACKET_LEN);
 		--rq->num;
 	}
 	return 0;
@@ -341,8 +362,10 @@ static void receive_buf(struct receive_queue *rq, void
*buf, unsigned int len)
 	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++;
-		if (vi->mergeable_rx_bufs || vi->big_packets)
+		if (vi->big_packets)
 			give_pages(rq, buf);
+		else if (vi->mergeable_rx_bufs)
+			put_page(virt_to_head_page(buf));
 		else
 			dev_kfree_skb(buf);
 		return;
@@ -352,19 +375,28 @@ static void receive_buf(struct receive_queue *rq, void
*buf, unsigned int len)
 		skb = buf;
 		len -= sizeof(struct virtio_net_hdr);
 		skb_trim(skb, len);
+	} else if (vi->mergeable_rx_bufs) {
+		struct page *page = virt_to_head_page(buf);
+		skb = page_to_skb(rq, page,
+				  (char *)buf - (char *)page_address(page),
+				  len, MAX_PACKET_LEN);
+		if (unlikely(!skb)) {
+			dev->stats.rx_dropped++;
+			put_page(page);
+			return;
+		}
+		if (receive_mergeable(rq, skb)) {
+			dev_kfree_skb(skb);
+			return;
+		}
 	} else {
 		page = buf;
-		skb = page_to_skb(rq, page, len);
+		skb = page_to_skb(rq, page, 0, len, PAGE_SIZE);
 		if (unlikely(!skb)) {
 			dev->stats.rx_dropped++;
 			give_pages(rq, page);
 			return;
 		}
-		if (vi->mergeable_rx_bufs)
-			if (receive_mergeable(rq, skb)) {
-				dev_kfree_skb(skb);
-				return;
-			}
 	}
 
 	hdr = skb_vnet_hdr(skb);
@@ -501,18 +533,28 @@ static int add_recvbuf_big(struct receive_queue *rq, gfp_t
gfp)
 
 static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
 {
-	struct page *page;
+	struct virtnet_info *vi = rq->vq->vdev->priv;
+	char *buf = NULL;
 	int err;
 
-	page = get_a_page(rq, gfp);
-	if (!page)
+	if (gfp & __GFP_WAIT) {
+		if (skb_page_frag_refill(MAX_PACKET_LEN, &vi->alloc_frag,
+					 gfp)) {
+			buf = (char *)page_address(vi->alloc_frag.page) +
+			      vi->alloc_frag.offset;
+			get_page(vi->alloc_frag.page);
+			vi->alloc_frag.offset += MAX_PACKET_LEN;
+		}
+	} else {
+		buf = netdev_alloc_frag(MAX_PACKET_LEN);
+	}
+	if (!buf)
 		return -ENOMEM;
 
-	sg_init_one(rq->sg, page_address(page), PAGE_SIZE);
-
-	err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, page, gfp);
+	sg_init_one(rq->sg, buf, MAX_PACKET_LEN);
+	err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, buf, gfp);
 	if (err < 0)
-		give_pages(rq, page);
+		put_page(virt_to_head_page(buf));
 
 	return err;
 }
@@ -1343,8 +1385,10 @@ static void free_unused_bufs(struct virtnet_info *vi)
 		struct virtqueue *vq = vi->rq[i].vq;
 
 		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
-			if (vi->mergeable_rx_bufs || vi->big_packets)
+			if (vi->big_packets)
 				give_pages(&vi->rq[i], buf);
+			else if (vi->mergeable_rx_bufs)
+				put_page(virt_to_head_page(buf));
 			else
 				dev_kfree_skb(buf);
 			--vi->rq[i].num;
@@ -1650,6 +1694,8 @@ free_recv_bufs:
 free_vqs:
 	cancel_delayed_work_sync(&vi->refill);
 	virtnet_del_vqs(vi);
+	if (vi->alloc_frag.page)
+		put_page(vi->alloc_frag.page);
 free_index:
 	free_percpu(vi->vq_index);
 free_stats:
@@ -1685,6 +1731,8 @@ static void virtnet_remove(struct virtio_device *vdev)
 	unregister_netdev(vi->dev);
 
 	remove_vq_common(vi);
+	if (vi->alloc_frag.page)
+		put_page(vi->alloc_frag.page);
 
 	flush_work(&vi->config_work);
 
-- 
1.8.4.1

On Mon, 2013-10-28 at 15:44 -0700, Michael Dalton wrote:
> The virtio_net driver's mergeable receive buffer allocator
> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> is > 4KB but only ~1500 bytes of the buffer is used to store
> packet data, reducing the effective TCP window size
> substantially. This patch addresses the performance concerns
> with mergeable receive buffers by allocating MTU-sized packet
> buffers using page frag allocators. If more than MAX_SKB_FRAGS
> buffers are needed, the SKB frag_list is used.
> 
> Signed-off-by: Michael Dalton <mwdalton at google.com>
> ---
Signed-off-by: Eric Dumazet <edumazet at google.com>

Daniel & Francesco, this should address the performance problem you
tried to address with ("tcp: rcvbuf autotuning improvements") 

( http://www.spinics.net/lists/netdev/msg252642.html )

Thanks !

Michael Dalton <mwdalton at google.com> writes:
> The virtio_net driver's mergeable receive buffer allocator
> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> is > 4KB but only ~1500 bytes of the buffer is used to store
> packet data, reducing the effective TCP window size
> substantially. This patch addresses the performance concerns
> with mergeable receive buffers by allocating MTU-sized packet
> buffers using page frag allocators. If more than MAX_SKB_FRAGS
> buffers are needed, the SKB frag_list is used.
>
> Signed-off-by: Michael Dalton <mwdalton at google.com>
Hi Michael,

        Nice work!  Just one comment.  Your patch highlights the
anachronistic name MAX_PACKET_LEN: it was from the original
implementation which only supported 1500 byte packets, and only used in
one place.

Please apply a first patch like this, then come up with a new constant
name (GOOD_PACKET_LEN?) for that value.  Because it's not the maximum
packet we can receive for mergable buffers.

Thanks,
Rusty.

Subject: virtio_net: remove anachronistic MAX_PACKET_LEN constant.
From: Rusty Russell <rusty at rustcorp.com.au>

The initial implementation of virtio_net only allowed ethernet-style
MTU packets; with more recent features this isn't true.  Move the
constant into the function where it's used.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 057ea13..dcbfccd 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -35,8 +35,6 @@ static bool csum = true, gso = true;
 module_param(csum, bool, 0444);
 module_param(gso, bool, 0444);
 
-/* FIXME: MTU in config. */
-#define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
 #define GOOD_COPY_LEN	128
 
 #define VIRTNET_DRIVER_VERSION "1.0.0"
@@ -434,12 +432,13 @@ static int add_recvbuf_small(struct receive_queue *rq,
gfp_t gfp)
 	struct sk_buff *skb;
 	struct skb_vnet_hdr *hdr;
 	int err;
+	const int len = ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN;
 
-	skb = __netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN, gfp);
+	skb = __netdev_alloc_skb_ip_align(vi->dev, len, gfp);
 	if (unlikely(!skb))
 		return -ENOMEM;
 
-	skb_put(skb, MAX_PACKET_LEN);
+	skb_put(skb, len);
 
 	hdr = skb_vnet_hdr(skb);
 	sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);

From: Eric Dumazet <eric.dumazet at gmail.com>
Date: Mon, 28 Oct 2013 16:19:49 -0700
> On Mon, 2013-10-28 at 15:44 -0700, Michael Dalton wrote:
>> The virtio_net driver's mergeable receive buffer allocator
>> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
>> is > 4KB but only ~1500 bytes of the buffer is used to store
>> packet data, reducing the effective TCP window size
>> substantially. This patch addresses the performance concerns
>> with mergeable receive buffers by allocating MTU-sized packet
>> buffers using page frag allocators. If more than MAX_SKB_FRAGS
>> buffers are needed, the SKB frag_list is used.
>> 
>> Signed-off-by: Michael Dalton <mwdalton at google.com>
>> ---
> 
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> 
> Daniel & Francesco, this should address the performance problem you
> tried to address with ("tcp: rcvbuf autotuning improvements") 
> 
> ( http://www.spinics.net/lists/netdev/msg252642.html )
Applied, thanks everyone.

On 10/29/2013 06:44 AM, Michael Dalton wrote:
> The virtio_net driver's mergeable receive buffer allocator
> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> is > 4KB but only ~1500 bytes of the buffer is used to store
> packet data, reducing the effective TCP window size
> substantially. This patch addresses the performance concerns
> with mergeable receive buffers by allocating MTU-sized packet
> buffers using page frag allocators. If more than MAX_SKB_FRAGS
> buffers are needed, the SKB frag_list is used.
>
> Signed-off-by: Michael Dalton <mwdalton at google.com>
Do you have any perf numberf of this patch? Have a glance of the patch,
looks like it will hurt the performance of large GSO packet. Always
allocating 1500 bytes mean a virtqueue can only hold about 4 full size
gso packets, and frag list will introduce extra overheads on skb
allocation. I just test it on my desktop, performance of full size gso
packet drops about 10%.

Mergeable buffer is a good balance between performance and the space it
occupies. If you just want a ~1500 bytes packet to be received, you can
just disable the mergeable buffer and just use small packet.

Alternatively, a simpler way is just use build_skb() and head frag to
build the skb directly on the page for medium size packets (small
packets were still copied) like following patch (may need more work
since vnet header is too short for NET_SKB_PAD). This can reduce the
truesize while keep the performance for large GSO packet.

---
 drivers/net/virtio_net.c |   48
++++++++++++++++++++++++++++++---------------
 1 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3c23fdc..4c7ad89 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -239,16 +239,12 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
     struct skb_vnet_hdr *hdr;
     unsigned int copy, hdr_len, offset;
     char *p;
+    int skb_size = SKB_DATA_ALIGN(len) +
+               SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+    bool frag;
 
     p = page_address(page);
 
-    /* copy small packet so we can reuse these pages for small data */
-    skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
-    if (unlikely(!skb))
-        return NULL;
-
-    hdr = skb_vnet_hdr(skb);
-
     if (vi->mergeable_rx_bufs) {
         hdr_len = sizeof hdr->mhdr;
         offset = hdr_len;
@@ -257,18 +253,38 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
         offset = sizeof(struct padded_vnet_hdr);
     }
 
-    memcpy(hdr, p, hdr_len);
-
     len -= hdr_len;
     p += offset;
 
-    copy = len;
-    if (copy > skb_tailroom(skb))
-        copy = skb_tailroom(skb);
-    memcpy(skb_put(skb, copy), p, copy);
+    frag = (len > GOOD_COPY_LEN) && (skb_size <= PAGE_SIZE)
&&
+        vi->mergeable_rx_bufs;
+    if (frag) {
+        skb = build_skb(page_address(page), skb_size);
+        if (unlikely(!skb))
+            return NULL;
+
+        skb_reserve(skb, offset);
+        skb_put(skb, len);
+        len = 0;
+    } else {
+        /* copy small packet so we can reuse these pages for small data
+         */
+        skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
+        if (unlikely(!skb))
+            return NULL;
+
+        copy = len;
+        if (copy > skb_tailroom(skb))
+            copy = skb_tailroom(skb);
+        memcpy(skb_put(skb, copy), p, copy);
+
+        len -= copy;
+        offset += copy;
+    }
+
+    hdr = skb_vnet_hdr(skb);
 
-    len -= copy;
-    offset += copy;
+    memcpy(hdr, page_address(page), hdr_len);
 
     /*
      * Verify that we can indeed put this data into a skb.
@@ -288,7 +304,7 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
         offset = 0;
     }
 
-    if (page)
+    if (page && !frag)
         give_pages(rq, page);
 
     return skb;
-- 
1.7.1

On 10/29/2013 12:19 AM, Eric Dumazet wrote:
> On Mon, 2013-10-28 at 15:44 -0700, Michael Dalton wrote:
>> The virtio_net driver's mergeable receive buffer allocator
>> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
>> is > 4KB but only ~1500 bytes of the buffer is used to store
>> packet data, reducing the effective TCP window size
>> substantially. This patch addresses the performance concerns
>> with mergeable receive buffers by allocating MTU-sized packet
>> buffers using page frag allocators. If more than MAX_SKB_FRAGS
>> buffers are needed, the SKB frag_list is used.
>>
>> Signed-off-by: Michael Dalton <mwdalton at google.com>
>> ---
>
> Signed-off-by: Eric Dumazet <edumazet at google.com>
>
> Daniel & Francesco, this should address the performance problem you
> tried to address with ("tcp: rcvbuf autotuning improvements")
That's awesome, thanks everyone !
> ( http://www.spinics.net/lists/netdev/msg252642.html )
>
> Thanks !

On Mon, Oct 28, 2013 at 10:44 PM, Michael Dalton <mwdalton at google.com>
wrote:
> The virtio_net driver's mergeable receive buffer allocator
> uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> is > 4KB but only ~1500 bytes of the buffer is used to store
> packet data, reducing the effective TCP window size
> substantially. This patch addresses the performance concerns
> with mergeable receive buffers by allocating MTU-sized packet
> buffers using page frag allocators. If more than MAX_SKB_FRAGS
> buffers are needed, the SKB frag_list is used.
This looks really good, just one nit below -- should we add MTU-sized
packets, or add MTU+sizeof(virtnet_hdr)-sized packets?

Reviewed-by: Eric Northup <digitaleric at google.com>
>
> Signed-off-by: Michael Dalton <mwdalton at google.com>
> ---
>  drivers/net/virtio_net.c | 164
++++++++++++++++++++++++++++++-----------------
>  1 file changed, 106 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9fbdfcd..113ee93 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -124,6 +124,11 @@ struct virtnet_info {
>         /* Lock for config space updates */
>         struct mutex config_lock;
>
> +       /* Page_frag for GFP_KERNEL packet buffer allocation when we run
> +        * low on memory.
> +        */
> +       struct page_frag alloc_frag;
> +
>         /* Does the affinity hint is set for virtqueues? */
>         bool affinity_hint_set;
>
> @@ -217,33 +222,18 @@ static void skb_xmit_done(struct virtqueue *vq)
>         netif_wake_subqueue(vi->dev, vq2txq(vq));
>  }
>
> -static void set_skb_frag(struct sk_buff *skb, struct page *page,
> -                        unsigned int offset, unsigned int *len)
> -{
> -       int size = min((unsigned)PAGE_SIZE - offset, *len);
> -       int i = skb_shinfo(skb)->nr_frags;
> -
> -       __skb_fill_page_desc(skb, i, page, offset, size);
> -
> -       skb->data_len += size;
> -       skb->len += size;
> -       skb->truesize += PAGE_SIZE;
> -       skb_shinfo(skb)->nr_frags++;
> -       skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
> -       *len -= size;
> -}
> -
>  /* Called from bottom half context */
>  static struct sk_buff *page_to_skb(struct receive_queue *rq,
> -                                  struct page *page, unsigned int len)
> +                                  struct page *page, unsigned int offset,
> +                                  unsigned int len, unsigned int truesize)
>  {
>         struct virtnet_info *vi = rq->vq->vdev->priv;
>         struct sk_buff *skb;
>         struct skb_vnet_hdr *hdr;
> -       unsigned int copy, hdr_len, offset;
> +       unsigned int copy, hdr_len, hdr_padded_len;
>         char *p;
>
> -       p = page_address(page);
> +       p = page_address(page) + offset;
>
>         /* copy small packet so we can reuse these pages for small data */
>         skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> @@ -254,16 +244,17 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
>
>         if (vi->mergeable_rx_bufs) {
>                 hdr_len = sizeof hdr->mhdr;
> -               offset = hdr_len;
> +               hdr_padded_len = sizeof hdr->mhdr;
>         } else {
>                 hdr_len = sizeof hdr->hdr;
> -               offset = sizeof(struct padded_vnet_hdr);
> +               hdr_padded_len = sizeof(struct padded_vnet_hdr);
>         }
>
>         memcpy(hdr, p, hdr_len);
>
>         len -= hdr_len;
> -       p += offset;
> +       offset += hdr_padded_len;
> +       p += hdr_padded_len;
>
>         copy = len;
>         if (copy > skb_tailroom(skb))
> @@ -273,6 +264,14 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
>         len -= copy;
>         offset += copy;
>
> +       if (vi->mergeable_rx_bufs) {
> +               if (len)
> +                       skb_add_rx_frag(skb, 0, page, offset, len,
truesize);
> +               else
> +                       put_page(page);
> +               return skb;
> +       }
> +
>         /*
>          * Verify that we can indeed put this data into a skb.
>          * This is here to handle cases when the device erroneously
> @@ -284,9 +283,12 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
>                 dev_kfree_skb(skb);
>                 return NULL;
>         }
> -
> +       BUG_ON(offset >= PAGE_SIZE);
>         while (len) {
> -               set_skb_frag(skb, page, offset, &len);
> +               unsigned int frag_size = min((unsigned)PAGE_SIZE - offset,
len);
> +               skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
offset,
> +                               frag_size, truesize);
> +               len -= frag_size;
>                 page = (struct page *)page->private;
>                 offset = 0;
>         }
> @@ -297,33 +299,52 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
>         return skb;
>  }
>
> -static int receive_mergeable(struct receive_queue *rq, struct sk_buff
*skb)
> +static int receive_mergeable(struct receive_queue *rq, struct sk_buff
*head_skb)
>  {
> -       struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
> +       struct skb_vnet_hdr *hdr = skb_vnet_hdr(head_skb);
> +       struct sk_buff *curr_skb = head_skb;
> +       char *buf;
>         struct page *page;
> -       int num_buf, i, len;
> +       int num_buf, len;
>
>         num_buf = hdr->mhdr.num_buffers;
>         while (--num_buf) {
> -               i = skb_shinfo(skb)->nr_frags;
> -               if (i >= MAX_SKB_FRAGS) {
> -                       pr_debug("%s: packet too long\n",
skb->dev->name);
> -                       skb->dev->stats.rx_length_errors++;
> -                       return -EINVAL;
> -               }
> -               page = virtqueue_get_buf(rq->vq, &len);
> -               if (!page) {
> +               int num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
> +               buf = virtqueue_get_buf(rq->vq, &len);
> +               if (unlikely(!buf)) {
>                         pr_debug("%s: rx error: %d buffers
missing\n",
> -                                skb->dev->name,
hdr->mhdr.num_buffers);
> -                       skb->dev->stats.rx_length_errors++;
> +                                head_skb->dev->name,
hdr->mhdr.num_buffers);
> +                       head_skb->dev->stats.rx_length_errors++;
>                         return -EINVAL;
>                 }
> -
> -               if (len > PAGE_SIZE)
> -                       len = PAGE_SIZE;
> -
> -               set_skb_frag(skb, page, 0, &len);
> -
> +               if (unlikely(len > MAX_PACKET_LEN)) {
> +                       pr_debug("%s: rx error: merge buffer too
long\n",
> +                                head_skb->dev->name);
> +                       len = MAX_PACKET_LEN;
> +               }
> +               if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
> +                       struct sk_buff *nskb = alloc_skb(0, GFP_ATOMIC);
> +                       if (unlikely(!nskb)) {
> +                               head_skb->dev->stats.rx_dropped++;
> +                               return -ENOMEM;
> +                       }
> +                       if (curr_skb == head_skb)
> +                               skb_shinfo(curr_skb)->frag_list = nskb;
> +                       else
> +                               curr_skb->next = nskb;
> +                       curr_skb = nskb;
> +                       head_skb->truesize += nskb->truesize;
> +                       num_skb_frags = 0;
> +               }
> +               if (curr_skb != head_skb) {
> +                       head_skb->data_len += len;
> +                       head_skb->len += len;
> +                       head_skb->truesize += MAX_PACKET_LEN;
> +               }
> +               page = virt_to_head_page(buf);
> +               skb_add_rx_frag(curr_skb, num_skb_frags, page,
> +                               buf - (char *)page_address(page), len,
> +                               MAX_PACKET_LEN);
>                 --rq->num;
>         }
>         return 0;
> @@ -341,8 +362,10 @@ static void receive_buf(struct receive_queue *rq, void
*buf, unsigned int len)
>         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++;
> -               if (vi->mergeable_rx_bufs || vi->big_packets)
> +               if (vi->big_packets)
>                         give_pages(rq, buf);
> +               else if (vi->mergeable_rx_bufs)
> +                       put_page(virt_to_head_page(buf));
>                 else
>                         dev_kfree_skb(buf);
>                 return;
> @@ -352,19 +375,28 @@ static void receive_buf(struct receive_queue *rq,
void *buf, unsigned int len)
>                 skb = buf;
>                 len -= sizeof(struct virtio_net_hdr);
>                 skb_trim(skb, len);
> +       } else if (vi->mergeable_rx_bufs) {
> +               struct page *page = virt_to_head_page(buf);
> +               skb = page_to_skb(rq, page,
> +                                 (char *)buf - (char *)page_address(page),
> +                                 len, MAX_PACKET_LEN);
> +               if (unlikely(!skb)) {
> +                       dev->stats.rx_dropped++;
> +                       put_page(page);
> +                       return;
> +               }
> +               if (receive_mergeable(rq, skb)) {
> +                       dev_kfree_skb(skb);
> +                       return;
> +               }
>         } else {
>                 page = buf;
> -               skb = page_to_skb(rq, page, len);
> +               skb = page_to_skb(rq, page, 0, len, PAGE_SIZE);
>                 if (unlikely(!skb)) {
>                         dev->stats.rx_dropped++;
>                         give_pages(rq, page);
>                         return;
>                 }
> -               if (vi->mergeable_rx_bufs)
> -                       if (receive_mergeable(rq, skb)) {
> -                               dev_kfree_skb(skb);
> -                               return;
> -                       }
>         }
>
>         hdr = skb_vnet_hdr(skb);
> @@ -501,18 +533,28 @@ static int add_recvbuf_big(struct receive_queue *rq,
gfp_t gfp)
>
>  static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
>  {
> -       struct page *page;
> +       struct virtnet_info *vi = rq->vq->vdev->priv;
> +       char *buf = NULL;
>         int err;
>
> -       page = get_a_page(rq, gfp);
> -       if (!page)
> +       if (gfp & __GFP_WAIT) {
Shouldn't this be MAX_PACKET_LEN + sizeof(virtio_net_hdr_mrg_rxbuf) ?

That way, we can receive an MTU-sized packet while only consuming a
single queue entry.
> +               if (skb_page_frag_refill(MAX_PACKET_LEN,
&vi->alloc_frag,
> +                                        gfp)) {
> +                       buf = (char *)page_address(vi->alloc_frag.page)
+
> +                             vi->alloc_frag.offset;
> +                       get_page(vi->alloc_frag.page);
> +                       vi->alloc_frag.offset += MAX_PACKET_LEN;
> +               }
> +       } else {
> +               buf = netdev_alloc_frag(MAX_PACKET_LEN);
> +       }
> +       if (!buf)
>                 return -ENOMEM;
>
> -       sg_init_one(rq->sg, page_address(page), PAGE_SIZE);
> -
> -       err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, page, gfp);
> +       sg_init_one(rq->sg, buf, MAX_PACKET_LEN);
> +       err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, buf, gfp);
>         if (err < 0)
> -               give_pages(rq, page);
> +               put_page(virt_to_head_page(buf));
>
>         return err;
>  }
> @@ -1343,8 +1385,10 @@ static void free_unused_bufs(struct virtnet_info
*vi)
>                 struct virtqueue *vq = vi->rq[i].vq;
>
>                 while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> -                       if (vi->mergeable_rx_bufs || vi->big_packets)
> +                       if (vi->big_packets)
>                                 give_pages(&vi->rq[i], buf);
> +                       else if (vi->mergeable_rx_bufs)
> +                               put_page(virt_to_head_page(buf));
>                         else
>                                 dev_kfree_skb(buf);
>                         --vi->rq[i].num;
> @@ -1650,6 +1694,8 @@ free_recv_bufs:
>  free_vqs:
>         cancel_delayed_work_sync(&vi->refill);
>         virtnet_del_vqs(vi);
> +       if (vi->alloc_frag.page)
> +               put_page(vi->alloc_frag.page);
>  free_index:
>         free_percpu(vi->vq_index);
>  free_stats:
> @@ -1685,6 +1731,8 @@ static void virtnet_remove(struct virtio_device
*vdev)
>         unregister_netdev(vi->dev);
>
>         remove_vq_common(vi);
> +       if (vi->alloc_frag.page)
> +               put_page(vi->alloc_frag.page);
>
>         flush_work(&vi->config_work);
>
> --
> 1.8.4.1
>
> _______________________________________________
> Virtualization mailing list
> Virtualization at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Agreed Eric, the buffer size should be increased so that we can accommodate a
MTU-sized packet + mergeable virtio net header in a single buffer. I will send
a patch to fix shortly cleaning up the #define headers as Rusty indicated and
increasing the buffer size slightly by VirtioNet header size bytes per Eric.

Jason, I'll followup with you directly - I'd like to know your exact
workload
(single steam or multi-stream netperf?), VM configuration, etc, and also see if
the nit that Erichas pointed out affects your results.  It is also
worth noting that
we may want to tune the queue sizes for your benchmarks, e.g, by reducing
buffer size from 4KB to MTU-sized but keeping queue length constant, we're
implicitly decreasing the number of bytes stored in the VirtioQueue for the
VirtioNet device, so increasing the queue size may help.

Best,

Mike

On Tue, Oct 29, 2013 at 06:44:40PM +0000, Eric Northup
wrote:
> On Mon, Oct 28, 2013 at 10:44 PM, Michael Dalton <mwdalton at
google.com> wrote:
> > The virtio_net driver's mergeable receive buffer allocator
> > uses 4KB packet buffers. For MTU-sized traffic, SKB truesize
> > is > 4KB but only ~1500 bytes of the buffer is used to store
> > packet data, reducing the effective TCP window size
> > substantially. This patch addresses the performance concerns
> > with mergeable receive buffers by allocating MTU-sized packet
> > buffers using page frag allocators. If more than MAX_SKB_FRAGS
> > buffers are needed, the SKB frag_list is used.
> 
> This looks really good, just one nit below -- should we add MTU-sized
> packets, or add MTU+sizeof(virtnet_hdr)-sized packets?
> 
> Reviewed-by: Eric Northup <digitaleric at google.com>
Yea, except it increases the typical number of packets per TSO
packet by a factor of 2.5, so it's almost sure to hurt performance
for some workloads.

Maybe the right thing to do is to pass a mix of small and big
buffers to the device. Device can pick the right size depending
on the size of the packet it has.

What to do for existing devices? I'm not sure. tcp rcv buf is at
least tunable.  I guess we could choose the buffer size depending on
default rcv buf. And/or maybe a module parameter ...
> >
> > Signed-off-by: Michael Dalton <mwdalton at google.com>
> > ---
> >  drivers/net/virtio_net.c | 164
++++++++++++++++++++++++++++++-----------------
> >  1 file changed, 106 insertions(+), 58 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 9fbdfcd..113ee93 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -124,6 +124,11 @@ struct virtnet_info {
> >         /* Lock for config space updates */
> >         struct mutex config_lock;
> >
> > +       /* Page_frag for GFP_KERNEL packet buffer allocation when we
run
> > +        * low on memory.
> > +        */
> > +       struct page_frag alloc_frag;
> > +
> >         /* Does the affinity hint is set for virtqueues? */
> >         bool affinity_hint_set;
> >
> > @@ -217,33 +222,18 @@ static void skb_xmit_done(struct virtqueue *vq)
> >         netif_wake_subqueue(vi->dev, vq2txq(vq));
> >  }
> >
> > -static void set_skb_frag(struct sk_buff *skb, struct page *page,
> > -                        unsigned int offset, unsigned int *len)
> > -{
> > -       int size = min((unsigned)PAGE_SIZE - offset, *len);
> > -       int i = skb_shinfo(skb)->nr_frags;
> > -
> > -       __skb_fill_page_desc(skb, i, page, offset, size);
> > -
> > -       skb->data_len += size;
> > -       skb->len += size;
> > -       skb->truesize += PAGE_SIZE;
> > -       skb_shinfo(skb)->nr_frags++;
> > -       skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
> > -       *len -= size;
> > -}
> > -
> >  /* Called from bottom half context */
> >  static struct sk_buff *page_to_skb(struct receive_queue *rq,
> > -                                  struct page *page, unsigned int
len)
> > +                                  struct page *page, unsigned int
offset,
> > +                                  unsigned int len, unsigned int
truesize)
> >  {
> >         struct virtnet_info *vi = rq->vq->vdev->priv;
> >         struct sk_buff *skb;
> >         struct skb_vnet_hdr *hdr;
> > -       unsigned int copy, hdr_len, offset;
> > +       unsigned int copy, hdr_len, hdr_padded_len;
> >         char *p;
> >
> > -       p = page_address(page);
> > +       p = page_address(page) + offset;
> >
> >         /* copy small packet so we can reuse these pages for small
data */
> >         skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> > @@ -254,16 +244,17 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
> >
> >         if (vi->mergeable_rx_bufs) {
> >                 hdr_len = sizeof hdr->mhdr;
> > -               offset = hdr_len;
> > +               hdr_padded_len = sizeof hdr->mhdr;
> >         } else {
> >                 hdr_len = sizeof hdr->hdr;
> > -               offset = sizeof(struct padded_vnet_hdr);
> > +               hdr_padded_len = sizeof(struct padded_vnet_hdr);
> >         }
> >
> >         memcpy(hdr, p, hdr_len);
> >
> >         len -= hdr_len;
> > -       p += offset;
> > +       offset += hdr_padded_len;
> > +       p += hdr_padded_len;
> >
> >         copy = len;
> >         if (copy > skb_tailroom(skb))
> > @@ -273,6 +264,14 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
> >         len -= copy;
> >         offset += copy;
> >
> > +       if (vi->mergeable_rx_bufs) {
> > +               if (len)
> > +                       skb_add_rx_frag(skb, 0, page, offset, len,
truesize);
> > +               else
> > +                       put_page(page);
> > +               return skb;
> > +       }
> > +
> >         /*
> >          * Verify that we can indeed put this data into a skb.
> >          * This is here to handle cases when the device erroneously
> > @@ -284,9 +283,12 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
> >                 dev_kfree_skb(skb);
> >                 return NULL;
> >         }
> > -
> > +       BUG_ON(offset >= PAGE_SIZE);
> >         while (len) {
> > -               set_skb_frag(skb, page, offset, &len);
> > +               unsigned int frag_size = min((unsigned)PAGE_SIZE -
offset, len);
> > +               skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
page, offset,
> > +                               frag_size, truesize);
> > +               len -= frag_size;
> >                 page = (struct page *)page->private;
> >                 offset = 0;
> >         }
> > @@ -297,33 +299,52 @@ static struct sk_buff *page_to_skb(struct
receive_queue *rq,
> >         return skb;
> >  }
> >
> > -static int receive_mergeable(struct receive_queue *rq, struct sk_buff
*skb)
> > +static int receive_mergeable(struct receive_queue *rq, struct sk_buff
*head_skb)
> >  {
> > -       struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
> > +       struct skb_vnet_hdr *hdr = skb_vnet_hdr(head_skb);
> > +       struct sk_buff *curr_skb = head_skb;
> > +       char *buf;
> >         struct page *page;
> > -       int num_buf, i, len;
> > +       int num_buf, len;
> >
> >         num_buf = hdr->mhdr.num_buffers;
> >         while (--num_buf) {
> > -               i = skb_shinfo(skb)->nr_frags;
> > -               if (i >= MAX_SKB_FRAGS) {
> > -                       pr_debug("%s: packet too long\n",
skb->dev->name);
> > -                       skb->dev->stats.rx_length_errors++;
> > -                       return -EINVAL;
> > -               }
> > -               page = virtqueue_get_buf(rq->vq, &len);
> > -               if (!page) {
> > +               int num_skb_frags = skb_shinfo(curr_skb)->nr_frags;
> > +               buf = virtqueue_get_buf(rq->vq, &len);
> > +               if (unlikely(!buf)) {
> >                         pr_debug("%s: rx error: %d buffers
missing\n",
> > -                                skb->dev->name,
hdr->mhdr.num_buffers);
> > -                       skb->dev->stats.rx_length_errors++;
> > +                                head_skb->dev->name,
hdr->mhdr.num_buffers);
> > +                       head_skb->dev->stats.rx_length_errors++;
> >                         return -EINVAL;
> >                 }
> > -
> > -               if (len > PAGE_SIZE)
> > -                       len = PAGE_SIZE;
> > -
> > -               set_skb_frag(skb, page, 0, &len);
> > -
> > +               if (unlikely(len > MAX_PACKET_LEN)) {
> > +                       pr_debug("%s: rx error: merge buffer too
long\n",
> > +                                head_skb->dev->name);
> > +                       len = MAX_PACKET_LEN;
> > +               }
> > +               if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) {
> > +                       struct sk_buff *nskb = alloc_skb(0,
GFP_ATOMIC);
> > +                       if (unlikely(!nskb)) {
> > +                              
head_skb->dev->stats.rx_dropped++;
> > +                               return -ENOMEM;
> > +                       }
> > +                       if (curr_skb == head_skb)
> > +                               skb_shinfo(curr_skb)->frag_list =
nskb;
> > +                       else
> > +                               curr_skb->next = nskb;
> > +                       curr_skb = nskb;
> > +                       head_skb->truesize += nskb->truesize;
> > +                       num_skb_frags = 0;
> > +               }
> > +               if (curr_skb != head_skb) {
> > +                       head_skb->data_len += len;
> > +                       head_skb->len += len;
> > +                       head_skb->truesize += MAX_PACKET_LEN;
> > +               }
> > +               page = virt_to_head_page(buf);
> > +               skb_add_rx_frag(curr_skb, num_skb_frags, page,
> > +                               buf - (char *)page_address(page), len,
> > +                               MAX_PACKET_LEN);
> >                 --rq->num;
> >         }
> >         return 0;
> > @@ -341,8 +362,10 @@ static void receive_buf(struct receive_queue *rq,
void *buf, unsigned int len)
> >         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++;
> > -               if (vi->mergeable_rx_bufs || vi->big_packets)
> > +               if (vi->big_packets)
> >                         give_pages(rq, buf);
> > +               else if (vi->mergeable_rx_bufs)
> > +                       put_page(virt_to_head_page(buf));
> >                 else
> >                         dev_kfree_skb(buf);
> >                 return;
> > @@ -352,19 +375,28 @@ static void receive_buf(struct receive_queue
*rq, void *buf, unsigned int len)
> >                 skb = buf;
> >                 len -= sizeof(struct virtio_net_hdr);
> >                 skb_trim(skb, len);
> > +       } else if (vi->mergeable_rx_bufs) {
> > +               struct page *page = virt_to_head_page(buf);
> > +               skb = page_to_skb(rq, page,
> > +                                 (char *)buf - (char
*)page_address(page),
> > +                                 len, MAX_PACKET_LEN);
> > +               if (unlikely(!skb)) {
> > +                       dev->stats.rx_dropped++;
> > +                       put_page(page);
> > +                       return;
> > +               }
> > +               if (receive_mergeable(rq, skb)) {
> > +                       dev_kfree_skb(skb);
> > +                       return;
> > +               }
> >         } else {
> >                 page = buf;
> > -               skb = page_to_skb(rq, page, len);
> > +               skb = page_to_skb(rq, page, 0, len, PAGE_SIZE);
> >                 if (unlikely(!skb)) {
> >                         dev->stats.rx_dropped++;
> >                         give_pages(rq, page);
> >                         return;
> >                 }
> > -               if (vi->mergeable_rx_bufs)
> > -                       if (receive_mergeable(rq, skb)) {
> > -                               dev_kfree_skb(skb);
> > -                               return;
> > -                       }
> >         }
> >
> >         hdr = skb_vnet_hdr(skb);
> > @@ -501,18 +533,28 @@ static int add_recvbuf_big(struct receive_queue
*rq, gfp_t gfp)
> >
> >  static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> >  {
> > -       struct page *page;
> > +       struct virtnet_info *vi = rq->vq->vdev->priv;
> > +       char *buf = NULL;
> >         int err;
> >
> > -       page = get_a_page(rq, gfp);
> > -       if (!page)
> > +       if (gfp & __GFP_WAIT) {
> 
> Shouldn't this be MAX_PACKET_LEN + sizeof(virtio_net_hdr_mrg_rxbuf) ?
> 
> That way, we can receive an MTU-sized packet while only consuming a
> single queue entry.
> 
> > +               if (skb_page_frag_refill(MAX_PACKET_LEN,
&vi->alloc_frag,
> > +                                        gfp)) {
> > +                       buf = (char
*)page_address(vi->alloc_frag.page) +
> > +                             vi->alloc_frag.offset;
> > +                       get_page(vi->alloc_frag.page);
> > +                       vi->alloc_frag.offset += MAX_PACKET_LEN;
> > +               }
> > +       } else {
> > +               buf = netdev_alloc_frag(MAX_PACKET_LEN);
> > +       }
> > +       if (!buf)
> >                 return -ENOMEM;
> >
> > -       sg_init_one(rq->sg, page_address(page), PAGE_SIZE);
> > -
> > -       err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, page, gfp);
> > +       sg_init_one(rq->sg, buf, MAX_PACKET_LEN);
> > +       err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, buf, gfp);
> >         if (err < 0)
> > -               give_pages(rq, page);
> > +               put_page(virt_to_head_page(buf));
> >
> >         return err;
> >  }
> > @@ -1343,8 +1385,10 @@ static void free_unused_bufs(struct
virtnet_info *vi)
> >                 struct virtqueue *vq = vi->rq[i].vq;
> >
> >                 while ((buf = virtqueue_detach_unused_buf(vq)) !=
NULL) {
> > -                       if (vi->mergeable_rx_bufs ||
vi->big_packets)
> > +                       if (vi->big_packets)
> >                                 give_pages(&vi->rq[i], buf);
> > +                       else if (vi->mergeable_rx_bufs)
> > +                               put_page(virt_to_head_page(buf));
> >                         else
> >                                 dev_kfree_skb(buf);
> >                         --vi->rq[i].num;
> > @@ -1650,6 +1694,8 @@ free_recv_bufs:
> >  free_vqs:
> >         cancel_delayed_work_sync(&vi->refill);
> >         virtnet_del_vqs(vi);
> > +       if (vi->alloc_frag.page)
> > +               put_page(vi->alloc_frag.page);
> >  free_index:
> >         free_percpu(vi->vq_index);
> >  free_stats:
> > @@ -1685,6 +1731,8 @@ static void virtnet_remove(struct virtio_device
*vdev)
> >         unregister_netdev(vi->dev);
> >
> >         remove_vq_common(vi);
> > +       if (vi->alloc_frag.page)
> > +               put_page(vi->alloc_frag.page);
> >
> >         flush_work(&vi->config_work);
> >
> > --
> > 1.8.4.1
> >
> > _______________________________________________
> > Virtualization mailing list
> > Virtualization at lists.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/virtualization