netdev - Re: [PATCH net-next V2 02/11] net: Add skb_can

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Message-ID: <CAHS8izOUs-CEAzuBrE9rz_X5XHqJmWfrar8VtzrFJrS9=8zQLw@mail.gmail.com>
Date: Thu, 22 May 2025 16:09:35 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Tariq Toukan <tariqt@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Saeed Mahameed <saeedm@...dia.com>, 
	Leon Romanovsky <leon@...nel.org>, Richard Cochran <richardcochran@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, 
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Moshe Shemesh <moshe@...dia.com>, Mark Bloch <mbloch@...dia.com>, Gal Pressman <gal@...dia.com>, 
	Cosmin Ratiu <cratiu@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>
Subject: Re: [PATCH net-next V2 02/11] net: Add skb_can_coalesce for netmem

On Thu, May 22, 2025 at 2:43 PM Tariq Toukan <tariqt@...dia.com> wrote:
>
> From: Dragos Tatulea <dtatulea@...dia.com>
>
> Allow drivers that have moved over to netmem to do fragment coalescing.
>
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Signed-off-by: Cosmin Ratiu <cratiu@...dia.com>
> Signed-off-by: Tariq Toukan <tariqt@...dia.com>
> ---
>  include/linux/skbuff.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 5520524c93bf..e8e2860183b4 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -3887,6 +3887,18 @@ static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
>         return false;
>  }
>
> +static inline bool skb_can_coalesce_netmem(struct sk_buff *skb, int i,
> +                                          const netmem_ref netmem, int off)
> +{
> +       if (i) {
> +               const skb_frag_t *frag = &skb_shinfo(skb)->frags[i - 1];
> +
> +               return netmem == skb_frag_netmem(frag) &&
> +                      off == skb_frag_off(frag) + skb_frag_size(frag);
> +       }
> +       return false;
> +}
> +

Can we limit the code duplication by changing skb_can_coalesce to call
skb_can_coalesce_netmem? Or is that too bad for perf?

static inline bool skb_can_coalesce(struct sk_buff *skb, int i, const
struct page *page, int off) {
    skb_can_coalesce_netmem(skb, i, page_to_netmem(page), off);
}

It's always safe to cast a page to netmem.

-- 
Thanks,
Mina