Re: [PATCH net-next v7 1/2] xen networking: add basic XDP support for xen-netfront

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Mon,  4 May 2020 11:37:53 +0300
Denis Kirjanov <kda@linux-powerpc.org> wrote:

> +static int xennet_create_page_pool(struct netfront_queue *queue)
> +{
> +	int err;
> +	struct page_pool_params pp_params = {
> +		.order = 0,
> +		.flags = 0,
> +		.pool_size = NET_RX_RING_SIZE,
> +		.nid = NUMA_NO_NODE,
> +		.dev = &queue->info->netdev->dev,
> +		.offset = XDP_PACKET_HEADROOM,
> +		.max_len = XEN_PAGE_SIZE - XDP_PACKET_HEADROOM,
> +	};
> +
> +	queue->page_pool = page_pool_create(&pp_params);
> +	if (IS_ERR(queue->page_pool)) {
> +		 err = PTR_ERR(queue->page_pool);
> +		 queue->page_pool = NULL;
> +		 return err;
> +	}
> +
> +	err = xdp_rxq_info_reg(&queue->xdp_rxq, queue->info->netdev,
> +			       queue->id);
> +	if (err) {
> +		netdev_err(queue->info->netdev, "xdp_rxq_info_reg failed\n");
> +		goto err_free_pp;
> +	}
> +
> +	err = xdp_rxq_info_reg_mem_model(&queue->xdp_rxq,
> +					 MEM_TYPE_PAGE_ORDER0, NULL);

What!?! - You are creating a page_pool, but registering a MEM_TYPE_PAGE_ORDER0.

Have you even tested this?  The page_pool in-flight accounting will be
completely off.  This should show up when removing the page_pool again.

For driver developers do diagnose and catch stuff like this, we have
some bpftrace scripts that can help troubleshoot, here[1]:

[1] https://github.com/xdp-project/xdp-project/tree/master/areas/mem/bpftrace

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer