netdev - Re: [PATCH net] net: allow alloc_skb_with_frags() to use MAX_SKB

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Message-ID: <CANn89iLMd64djnN_KZi6y49zcd46Lg96uDO7YxkHaDsaJ=vdAw@mail.gmail.com>
Date: Mon, 15 Sep 2025 22:59:48 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Baron <jbaron@...mai.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net: allow alloc_skb_with_frags() to use MAX_SKB_FRAGS

On Mon, Sep 15, 2025 at 8:49 PM Jason Baron <jbaron@...mai.com> wrote:
>
> Currently, alloc_skb_with_frags() will only fill (MAX_SKB_FRAGS - 1)
> slots. I think it should use all MAX_SKB_FRAGS slots, as callers of
> alloc_skb_with_frags() will size their allocation of frags based
> on MAX_SKB_FRAGS.

Hi Jason

Interesting !

Could you give some details here, have you found this for af_unix users ?

They would still fail if no high order pages are available, for
allocations bigger than 64K ?

>
> Signed-off-by: Jason Baron <jbaron@...mai.com>
> ---
>  net/core/skbuff.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 23b776cd9879..df942aca0617 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -6669,7 +6669,7 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
>                 return NULL;
>
>         while (data_len) {
> -               if (nr_frags == MAX_SKB_FRAGS - 1)
> +               if (nr_frags == MAX_SKB_FRAGS)
>                         goto failure;
>                 while (order && PAGE_ALIGN(data_len) < (PAGE_SIZE << order))
>                         order--;
> --
> 2.25.1
>

We require a Fixes: tag for patches targeting net tree.

I suspect this would be

Fixes: 09c2c90705bb ("net: allow alloc_skb_with_frags() to allocate
bigger packets")

Thank you.