Re: [PATCH ipsec-next v12 14/16] xfrm: iptfs: add skb-fragment sharing code

[Steffen Klassert <steffen.klassert@secunet.com>]

On Mon, Oct 07, 2024 at 09:59:26AM -0400, Christian Hopps wrote:
> From: Christian Hopps <chopps@labn.net>
> 
> Avoid copying the inner packet data by sharing the skb data fragments
> from the output packet skb into new inner packet skb.
> 
> Signed-off-by: Christian Hopps <chopps@labn.net>
> ---
>  net/xfrm/xfrm_iptfs.c | 312 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 304 insertions(+), 8 deletions(-)
> 
> diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
> index 4c95656d7492..ef4c23159471 100644
> --- a/net/xfrm/xfrm_iptfs.c
> +++ b/net/xfrm/xfrm_iptfs.c
> @@ -81,6 +81,9 @@
>  #define XFRM_IPTFS_MIN_L3HEADROOM 128
>  #define XFRM_IPTFS_MIN_L2HEADROOM (L1_CACHE_BYTES > 64 ? 64 : 64 + 16)
>  
> +/* Min to try to share outer iptfs skb data vs copying into new skb */
> +#define IPTFS_PKT_SHARE_MIN 129
> +
>  #define NSECS_IN_USEC 1000
>  
>  #define IPTFS_HRTIMER_MODE HRTIMER_MODE_REL_SOFT
> @@ -236,10 +239,261 @@ static void iptfs_skb_head_to_frag(const struct sk_buff *skb, skb_frag_t *frag)
>  	skb_frag_fill_page_desc(frag, page, skb->data - addr, skb_headlen(skb));
>  }
>  
> +/**
> + * struct iptfs_skb_frag_walk - use to track a walk through fragments
> + * @fragi: current fragment index
> + * @past: length of data in fragments before @fragi
> + * @total: length of data in all fragments
> + * @nr_frags: number of fragments present in array
> + * @initial_offset: the value passed in to skb_prepare_frag_walk()
> + * @pp_recycle: copy of skb->pp_recycle
> + * @frags: the page fragments inc. room for head page
> + */
> +struct iptfs_skb_frag_walk {
> +	u32 fragi;
> +	u32 past;
> +	u32 total;
> +	u32 nr_frags;
> +	u32 initial_offset;
> +	bool pp_recycle;

This boll creates a 3 byte hole. Better to put it to the end.

> +	skb_frag_t frags[MAX_SKB_FRAGS + 1];
> +};