On Mon, Aug 25, 2025 at 09:53:37PM +0800, Jason Xing wrote:
> From: Jason Xing <kernelxing@xxxxxxxxxxx>
>
> Batch xmit mode needs to allocate and build skbs at one time. To avoid
> reinvent the wheel, use xsk_build_skb() as the second half process of
> the whole initialization of each skb.
>
> The original xsk_build_skb() itself allocates a new skb by calling
> sock_alloc_send_skb whether in copy mode or zerocopy mode. Add a new
> parameter allocated skb to let other callers to pass an already
> allocated skb to support later xmit batch feature. At that time,
> another building skb function will generate a new skb and pass it to
> xsk_build_skb() to finish the rest of building process, like
> initializing structures and copying data.
are you saying you were able to avoid sock_alloc_send_skb() calls for
batching approach and your socket memory accounting problems disappeared?
>
> Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> ---
> include/net/xdp_sock.h | 4 ++++
> net/xdp/xsk.c | 23 ++++++++++++++++-------
> 2 files changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index c2b05268b8ad..cbba880c27c3 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -123,6 +123,10 @@ struct xsk_tx_metadata_ops {
> void (*tmo_request_launch_time)(u64 launch_time, void *priv);
> };
>
> +
> +struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> + struct sk_buff *allocated_skb,
> + struct xdp_desc *desc);
why do you export this?
> #ifdef CONFIG_XDP_SOCKETS
>
> int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 173ad49379c3..213d6100e405 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -605,6 +605,7 @@ static void xsk_drop_skb(struct sk_buff *skb)
> }
>
> static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
> + struct sk_buff *allocated_skb,
> struct xdp_desc *desc)
> {
> struct xsk_buff_pool *pool = xs->pool;
> @@ -618,7 +619,10 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
> if (!skb) {
> hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(xs->dev->needed_headroom));
>
> - skb = sock_alloc_send_skb(&xs->sk, hr, 1, &err);
> + if (!allocated_skb)
> + skb = sock_alloc_send_skb(&xs->sk, hr, 1, &err);
> + else
> + skb = allocated_skb;
> if (unlikely(!skb))
> return ERR_PTR(err);
>
> @@ -657,8 +661,9 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
> return skb;
> }
>
> -static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> - struct xdp_desc *desc)
> +struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> + struct sk_buff *allocated_skb,
> + struct xdp_desc *desc)
> {
> struct xsk_tx_metadata *meta = NULL;
> struct net_device *dev = xs->dev;
> @@ -667,7 +672,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> int err;
>
> if (dev->priv_flags & IFF_TX_SKB_NO_LINEAR) {
> - skb = xsk_build_skb_zerocopy(xs, desc);
> + skb = xsk_build_skb_zerocopy(xs, allocated_skb, desc);
> if (IS_ERR(skb)) {
> err = PTR_ERR(skb);
> goto free_err;
> @@ -683,8 +688,12 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> first_frag = true;
>
> hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(dev->needed_headroom));
> - tr = dev->needed_tailroom;
> - skb = sock_alloc_send_skb(&xs->sk, hr + len + tr, 1, &err);
> + if (!allocated_skb) {
> + tr = dev->needed_tailroom;
> + skb = sock_alloc_send_skb(&xs->sk, hr + len + tr, 1, &err);
> + } else {
> + skb = allocated_skb;
> + }
> if (unlikely(!skb))
> goto free_err;
>
> @@ -818,7 +827,7 @@ static int __xsk_generic_xmit(struct sock *sk)
> goto out;
> }
>
> - skb = xsk_build_skb(xs, &desc);
> + skb = xsk_build_skb(xs, NULL, &desc);
> if (IS_ERR(skb)) {
> err = PTR_ERR(skb);
> if (err != -EOVERFLOW)
> --
> 2.41.3
>
