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Xuan Zhuo

2023-Mar-28 12:04 UTC

[PATCH net-next 1/8] virtio_net: mergeable xdp: put old page immediately

In the xdp implementation of virtio-net mergeable, it always checks
whether two page is used and a page is selected to release. This is
complicated for the processing of action, and be careful.

In the entire process, we have such principles:
* If xdp_page is used (PASS, TX, Redirect), then we release the old
  page.
* If it is a drop case, we will release two. The old page obtained from
  buf is release inside err_xdp, and xdp_page needs be relased by us.

But in fact, when we allocate a new page, we can release the old page
immediately. Then just one is using, we just need to release the new
page for drop case. On the drop path, err_xdp will release the variable
"page", so we only need to let "page" point to the new
xdp_page in
advance.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/net/virtio_net.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e2560b6f7980..4d2bf1ce0730 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1245,6 +1245,9 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			if (!xdp_page)
 				goto err_xdp;
 			offset = VIRTIO_XDP_HEADROOM;
+
+			put_page(page);
+			page = xdp_page;
 		} else if (unlikely(headroom < virtnet_get_headroom(vi))) {
 			xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
 						  sizeof(struct skb_shared_info));
@@ -1259,6 +1262,9 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			       page_address(page) + offset, len);
 			frame_sz = PAGE_SIZE;
 			offset = VIRTIO_XDP_HEADROOM;
+
+			put_page(page);
+			page = xdp_page;
 		} else {
 			xdp_page = page;
 		}
@@ -1278,8 +1284,6 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			if (unlikely(!head_skb))
 				goto err_xdp_frags;
 
-			if (unlikely(xdp_page != page))
-				put_page(page);
 			rcu_read_unlock();
 			return head_skb;
 		case XDP_TX:
@@ -1297,8 +1301,6 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 				goto err_xdp_frags;
 			}
 			*xdp_xmit |= VIRTIO_XDP_TX;
-			if (unlikely(xdp_page != page))
-				put_page(page);
 			rcu_read_unlock();
 			goto xdp_xmit;
 		case XDP_REDIRECT:
@@ -1307,8 +1309,6 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			if (err)
 				goto err_xdp_frags;
 			*xdp_xmit |= VIRTIO_XDP_REDIR;
-			if (unlikely(xdp_page != page))
-				put_page(page);
 			rcu_read_unlock();
 			goto xdp_xmit;
 		default:
@@ -1321,9 +1321,6 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			goto err_xdp_frags;
 		}
 err_xdp_frags:
-		if (unlikely(xdp_page != page))
-			__free_pages(xdp_page, 0);
-
 		if (xdp_buff_has_frags(&xdp)) {
 			shinfo = xdp_get_shared_info_from_buff(&xdp);
 			for (i = 0; i < shinfo->nr_frags; i++) {
-- 
2.32.0.3.g01195cf9f

Jason Wang

2023-Mar-31 09:01 UTC

head link

[PATCH net-next 1/8] virtio_net: mergeable xdp: put old page immediately

On Tue, Mar 28, 2023 at 8:04?PM Xuan Zhuo <xuanzhuo at linux.alibaba.com>
wrote:>
> In the xdp implementation of virtio-net mergeable, it always checks
> whether two page is used and a page is selected to release. This is
> complicated for the processing of action, and be careful.
>
> In the entire process, we have such principles:
> * If xdp_page is used (PASS, TX, Redirect), then we release the old
>   page.
> * If it is a drop case, we will release two. The old page obtained from
>   buf is release inside err_xdp, and xdp_page needs be relased by us.
>
> But in fact, when we allocate a new page, we can release the old page
> immediately. Then just one is using, we just need to release the new
> page for drop case. On the drop path, err_xdp will release the variable
> "page", so we only need to let "page" point to the new
xdp_page in
> advance.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e2560b6f7980..4d2bf1ce0730 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1245,6 +1245,9 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                         if (!xdp_page)
>                                 goto err_xdp;
>                         offset = VIRTIO_XDP_HEADROOM;
> +
> +                       put_page(page);
> +                       page = xdp_page;
>                 } else if (unlikely(headroom <
virtnet_get_headroom(vi))) {
>                         xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
>                                                   sizeof(struct
skb_shared_info));
> @@ -1259,6 +1262,9 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                                page_address(page) + offset, len);
>                         frame_sz = PAGE_SIZE;
>                         offset = VIRTIO_XDP_HEADROOM;
> +
> +                       put_page(page);
> +                       page = xdp_page;
>                 } else {
>                         xdp_page = page;
>                 }
While at this I would go a little further, just remove the above
assignment then we can use:

                data = page_address(page) + offset;

Which seems cleaner?

Thanks
> @@ -1278,8 +1284,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                         if (unlikely(!head_skb))
>                                 goto err_xdp_frags;
>
> -                       if (unlikely(xdp_page != page))
> -                               put_page(page);
>                         rcu_read_unlock();
>                         return head_skb;
>                 case XDP_TX:
> @@ -1297,8 +1301,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                                 goto err_xdp_frags;
>                         }
>                         *xdp_xmit |= VIRTIO_XDP_TX;
> -                       if (unlikely(xdp_page != page))
> -                               put_page(page);
>                         rcu_read_unlock();
>                         goto xdp_xmit;
>                 case XDP_REDIRECT:
> @@ -1307,8 +1309,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                         if (err)
>                                 goto err_xdp_frags;
>                         *xdp_xmit |= VIRTIO_XDP_REDIR;
> -                       if (unlikely(xdp_page != page))
> -                               put_page(page);
>                         rcu_read_unlock();
>                         goto xdp_xmit;
>                 default:
> @@ -1321,9 +1321,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>                         goto err_xdp_frags;
>                 }
>  err_xdp_frags:
> -               if (unlikely(xdp_page != page))
> -                       __free_pages(xdp_page, 0);
> -
>                 if (xdp_buff_has_frags(&xdp)) {
>                         shinfo = xdp_get_shared_info_from_buff(&xdp);
>                         for (i = 0; i < shinfo->nr_frags; i++) {
> --
> 2.32.0.3.g01195cf9f
>

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