netdev - Re: [PATCH 1/2] vsock/virtio: Coalesce only linear skb

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Message-ID: <ae564ab4-2dd2-4a12-a92c-b613fa430829@rbox.co>
Date: Sun, 11 Jan 2026 11:59:44 +0100
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>,
 Arseniy Krasnov <avkrasnov@...utedevices.com>, kvm@...r.kernel.org,
 virtualization@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] vsock/virtio: Coalesce only linear skb

On 1/9/26 17:18, Stefano Garzarella wrote:
> On Thu, Jan 08, 2026 at 10:54:54AM +0100, Michal Luczaj wrote:
...
>> @@ -1375,7 +1375,8 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
>> 		 * of a new message.
>> 		 */
>> 		if (skb->len < skb_tailroom(last_skb) &&
>> -		    !(le32_to_cpu(last_hdr->flags) & VIRTIO_VSOCK_SEQ_EOM)) {
>> +		    !(le32_to_cpu(last_hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) &&
>> +		    !skb_is_nonlinear(skb)) {
> 
> Why here? I mean we can do the check even early, something like this:
> 
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -1361,7 +1361,8 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
>           * to avoid wasting memory queueing the entire buffer with a small
>           * payload.
>           */
> -       if (len <= GOOD_COPY_LEN && !skb_queue_empty(&vvs->rx_queue)) {
> +       if (len <= GOOD_COPY_LEN && !skb_queue_empty(&vvs->rx_queue) &&
> +           !skb_is_nonlinear(skb)) {
>                  struct virtio_vsock_hdr *last_hdr;
>                  struct sk_buff *last_skb;

Right, can do. I've assumed skb being non-linear is the least likely in
this context.

> I would also add the reason in the comment before that to make it clear.

OK, sure.