netdev - Re: [PATCH v2 net-next] net: ethernet: enetc: unlock XDP

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Date:   Fri, 9 Dec 2022 02:58:21 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, claudiu.manoil@....com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, lorenzo.bianconi@...hat.com
Subject: Re: [PATCH v2 net-next] net: ethernet: enetc: unlock XDP_REDIRECT
 for XDP non-linear buffers

On Fri, Dec 09, 2022 at 01:19:44AM +0100, Lorenzo Bianconi wrote:
> Even if full XDP_REDIRECT is not supported yet for non-linear XDP buffers
> since we allow redirecting just into CPUMAPs, unlock XDP_REDIRECT for
> S/G XDP buffer and rely on XDP stack to properly take care of the
> frames.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
> Changes since v1:
> - drop Fixes tag
> - unlock XDP_REDIRECT
> - populate missing XDP metadata
> 
> Please note this patch is just compile tested
> ---

How would you like me to test this patch?

>  drivers/net/ethernet/freescale/enetc/enetc.c | 27 +++++++++-----------
>  1 file changed, 12 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index 8671591cb750..9fd15e1e692d 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -1412,6 +1412,16 @@ static void enetc_add_rx_buff_to_xdp(struct enetc_bdr *rx_ring, int i,
>  	/* To be used for XDP_TX */
>  	rx_swbd->len = size;
>  
> +	if (!xdp_buff_has_frags(xdp_buff)) {
> +		xdp_buff_set_frags_flag(xdp_buff);
> +		shinfo->xdp_frags_size = size;
> +	} else {
> +		shinfo->xdp_frags_size += size;
> +	}
> +
> +	if (page_is_pfmemalloc(rx_swbd->page))
> +		xdp_buff_set_frag_pfmemalloc(xdp_buff);
> +
>  	skb_frag_off_set(frag, rx_swbd->page_offset);
>  	skb_frag_size_set(frag, size);
>  	__skb_frag_set_page(frag, rx_swbd->page);
> @@ -1601,22 +1611,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
>  			}
>  			break;
>  		case XDP_REDIRECT:
> -			/* xdp_return_frame does not support S/G in the sense
> -			 * that it leaks the fragments (__xdp_return should not
> -			 * call page_frag_free only for the initial buffer).
> -			 * Until XDP_REDIRECT gains support for S/G let's keep
> -			 * the code structure in place, but dead. We drop the
> -			 * S/G frames ourselves to avoid memory leaks which
> -			 * would otherwise leave the kernel OOM.
> -			 */
> -			if (unlikely(cleaned_cnt - orig_cleaned_cnt != 1)) {
> -				enetc_xdp_drop(rx_ring, orig_i, i);
> -				rx_ring->stats.xdp_redirect_sg++;
> -				break;
> -			}
> -
>  			tmp_orig_i = orig_i;
> -
>  			while (orig_i != i) {
>  				enetc_flip_rx_buff(rx_ring,
>  						   &rx_ring->rx_swbd[orig_i]);
> @@ -1628,6 +1623,8 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
>  				enetc_xdp_free(rx_ring, tmp_orig_i, i);
>  			} else {
>  				xdp_redirect_frm_cnt++;
> +				if (xdp_buff_has_frags(&xdp_buff))
> +					rx_ring->stats.xdp_redirect_sg++;

Ideally we'd remove this counter altogether. Nothing interesting to see.

>  				rx_ring->stats.xdp_redirect++;
>  			}
>  		}
> -- 
> 2.38.1
>