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

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Message-ID: <Z7+UAA83/n9XgIdU@pop-os.localdomain>
Date: Wed, 26 Feb 2025 14:21:52 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Jakub Sitnicki <jakub@...udflare.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 Wed, Feb 26, 2025 at 02:49:17PM +0100, Jakub Sitnicki wrote:
> 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?

Kinda, or at least trying to save some space for the next patch. I am
not yet trying to reorder them to make it more packed, because it can
be a separate patch.

Thanks!