netdev - Re: [PATCH v2 net-next 1/2] net: veth: add page

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Date:   Sun, 23 Apr 2023 20:17:48 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, <netdev@...r.kernel.org>
CC:     <bpf@...r.kernel.org>, <lorenzo.bianconi@...hat.com>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <hawk@...nel.org>, <john.fastabend@...il.com>,
        <ast@...nel.org>, <daniel@...earbox.net>
Subject: Re: [PATCH v2 net-next 1/2] net: veth: add page_pool for page
 recycling

On 2023/4/23 2:54, Lorenzo Bianconi wrote:
>  struct veth_priv {
> @@ -727,17 +729,20 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
>  			goto drop;
>  
>  		/* Allocate skb head */
> -		page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
> +		page = page_pool_dev_alloc_pages(rq->page_pool);
>  		if (!page)
>  			goto drop;
>  
>  		nskb = build_skb(page_address(page), PAGE_SIZE);

If page pool is used with PP_FLAG_PAGE_FRAG, maybe there is some additional
improvement for the MTU 1500B case, it seem a 4K page is able to hold two skb.
And we can reduce the memory usage too, which is a significant saving if page
size is 64K.


>  		if (!nskb) {
> -			put_page(page);
> +			page_pool_put_full_page(rq->page_pool, page, true);
>  			goto drop;
>  		}
>  
>  		skb_reserve(nskb, VETH_XDP_HEADROOM);
> +		skb_copy_header(nskb, skb);
> +		skb_mark_for_recycle(nskb);
> +
>  		size = min_t(u32, skb->len, max_head_size);
>  		if (skb_copy_bits(skb, 0, nskb->data, size)) {
>  			consume_skb(nskb);
> @@ -745,7 +750,6 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
>  		}
>  		skb_put(nskb, size);
>  
> -		skb_copy_header(nskb, skb);
>  		head_off = skb_headroom(nskb) - skb_headroom(skb);
>  		skb_headers_offset_update(nskb, head_off);
>  
> @@ -754,7 +758,7 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
>  		len = skb->len - off;
>  
>  		for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
> -			page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
> +			page = page_pool_dev_alloc_pages(rq->page_pool);
>  			if (!page) {
>  				consume_skb(nskb);
>  				goto drop;
> @@ -1002,11 +1006,37 @@ static int veth_poll(struct napi_struct *napi, int budget)
>  	return done;
>  }
>  
> +static int veth_create_page_pool(struct veth_rq *rq)
> +{
> +	struct page_pool_params pp_params = {
> +		.order = 0,
> +		.pool_size = VETH_RING_SIZE,

It seems better to allocate different poo_size according to
the mtu, so that the best proformance is achiced using the
least memory?