netdev - Re: [PATCH v13 bpf-next 01/18] net: skbuff: add size metadata to skb_shared

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Date:   Tue, 7 Sep 2021 16:39:18 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     brouer@...hat.com, lorenzo.bianconi@...hat.com,
        davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, shayagr@...zon.com, john.fastabend@...il.com,
        dsahern@...nel.org, echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        tirthendu.sarkar@...el.com, toke@...hat.com
Subject: Re: [PATCH v13 bpf-next 01/18] net: skbuff: add size metadata to
 skb_shared_info for xdp



On 07/09/2021 14.35, Lorenzo Bianconi wrote:
> Introduce xdp_frags_tsize field in skb_shared_info data structure
> to store xdp_buff/xdp_frame truesize (xdp_frags_tsize will be used
> in xdp multi-buff support). In order to not increase skb_shared_info
> size we will use a hole due to skb_shared_info alignment.
> Introduce xdp_frags_size field in skb_shared_info data structure
> reusing gso_type field in order to store xdp_buff/xdp_frame paged size.
> xdp_frags_size will be used in xdp multi-buff support.
> 
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>   include/linux/skbuff.h | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 6bdb0db3e825..1abeba7ef82e 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -522,13 +522,17 @@ struct skb_shared_info {
>   	unsigned short	gso_segs;
>   	struct sk_buff	*frag_list;
>   	struct skb_shared_hwtstamps hwtstamps;
> -	unsigned int	gso_type;
> +	union {
> +		unsigned int	gso_type;
> +		unsigned int	xdp_frags_size;
> +	};
>   	u32		tskey;
>   
>   	/*
>   	 * Warning : all fields before dataref are cleared in __alloc_skb()
>   	 */
>   	atomic_t	dataref;
> +	unsigned int	xdp_frags_tsize;

I wonder if we could call this variable: xdp_frags_truesize.

As while reviewing patches I had to focus my eyes extra hard to tell the 
variables xdp_frags_size and xdp_frags_tsize from each-other.

--Jesper