netdev - Re: [RFC PATCH net-next 2/2] net: veth: Improving page pool recycling

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Date: Fri, 21 Jul 2023 20:18:13 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Liang Chen <liangchen.linux@...il.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>
CC: <hawk@...nel.org>, <ilias.apalodimas@...aro.org>, <daniel@...earbox.net>,
	<ast@...nel.org>, <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 2/2] net: veth: Improving page pool recycling

On 2023/7/19 15:29, Liang Chen wrote:

...

> 
> The reason behind is some skbs received from the veth peer are not page
> pool pages, and remain so after conversion to xdp frame. In order to not
> confusing __xdp_return with mixed regular pages and page pool pages, they
> are all converted to regular pages. So registering xdp memory model as
> MEM_TYPE_PAGE_SHARED is sufficient.
> 
> If we replace the above code with kfree_skb_partial, directly releasing
> the skb data structure, we can retain the original page pool page behavior.
> However, directly changing the xdp memory model to MEM_TYPE_PAGE_POOL is
> not a solution as explained above. Therefore, we introduced an additionally
> MEM_TYPE_PAGE_POOL model for each rq.
> 

...

> @@ -874,9 +862,9 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
>  		rcu_read_unlock();
>  		goto xdp_xmit;
>  	case XDP_REDIRECT:
> -		veth_xdp_get(xdp);
> -		consume_skb(skb);
> -		xdp->rxq->mem = rq->xdp_mem;
> +		xdp->rxq->mem = skb->pp_recycle ? rq->xdp_mem_pp : rq->xdp_mem;

I am not really familiar with the veth here, so some question here:
Is it possible that skbs received from the veth peer are also page pool pages?
Does using the local rq->xdp_mem_pp for page allocated from veth peer cause
some problem here? As there is type and id for a specific page_pool instance,
type may be the same, but I suppose id is not the same for veth and it's veth
peer.

> +		kfree_skb_partial(skb, true);
> +