netdev - Re: [Patch bpf-next 3/4] skmsg: use bitfields for struct sk

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Message-ID: <87ldtsu882.fsf@cloudflare.com>
Date: Wed, 26 Feb 2025 14:49:17 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org,  bpf@...r.kernel.org,  john.fastabend@...il.com,
  zhoufeng.zf@...edance.com,  zijianzhang@...edance.com,  Cong Wang
 <cong.wang@...edance.com>
Subject: Re: [Patch bpf-next 3/4] skmsg: use bitfields for struct sk_psock

On Sat, Feb 22, 2025 at 10:30 AM -08, Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
>
> psock->eval can only have 4 possible values, make it 8-bit is
> sufficient.
>
> psock->redir_ingress is just a boolean, using 1 bit is enough.
>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---
>  include/linux/skmsg.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index bf28ce9b5fdb..beaf79b2b68b 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -85,8 +85,8 @@ struct sk_psock {
>  	struct sock			*sk_redir;
>  	u32				apply_bytes;
>  	u32				cork_bytes;
> -	u32				eval;
> -	bool				redir_ingress; /* undefined if sk_redir is null */
> +	unsigned int			eval : 8;
> +	unsigned int			redir_ingress : 1; /* undefined if sk_redir is null */
>  	struct sk_msg			*cork;
>  	struct sk_psock_progs		progs;
>  #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)

Are you doing this bit packing to create a hole big enough to fit
another u32 introduced in the next patch?