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

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Date:   Fri, 21 Apr 2023 20:22:30 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        toke@...hat.com, mtahhan@...hat.com, lorenzo.bianconi@...hat.com
Subject: Re: [PATCH net-next 1/2] net: veth: add page_pool for page
 recycling

On Thu, 20 Apr 2023 13:16:21 +0200 Lorenzo Bianconi wrote:
> @@ -727,17 +729,21 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
>  			goto drop;
>  
>  		/* Allocate skb head */
> -		page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
> +		if (rq->page_pool)

There's some condition under which we can get to XDP enabled but no
pool?

> +			page = page_pool_dev_alloc_pages(rq->page_pool);
>  		if (!page)
>  			goto drop;
>  
>  		nskb = build_skb(page_address(page), PAGE_SIZE);
>  		if (!nskb) {
> -			put_page(page);
> +			page_pool_put_full_page(rq->page_pool, page, false);

You can recycle direct, AFAIU the basic rule of thumb is that it's
always safe to recycle direct from the context which allocates from
the pool.

>  			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);
> @@ -745,16 +751,17 @@ 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);
>  
>  		/* Allocate paged area of new skb */
>  		off = size;
>  		len = skb->len - off;
> +		page = NULL;

Why do you clear the page pointer?

-- 
pw-bot: cr