Subject: Re: [PATCH net-next 4/5] net: skbuff: push nf_trace down the bitfield

From: Pablo Neira Ayuso <[email-masked]>
Date: Sat, 15 Apr 2023 10:31:19 +0200

On Fri, Apr 14, 2023 at 09:01:04AM -0700, Jakub Kicinski wrote:
> nf_trace is a debug feature, AFAIU, and yet it sits oddly
> high in the sk_buff bitfield. Move it down, pushing up
> dst_pending_confirm and inner_protocol_type.
> 
> Next change will make nf_trace optional (under Kconfig)
> and all optional fields should be placed after 2b fields
> to avoid 2b fields straddling bytes.
> 
> dst_pending_confirm is L3, so it makes sense next to ignore_df.
> inner_protocol_type goes up just to keep the balance.

Well, yes, this is indeed a debug feature.

But if only one single container enables debugging, this cache line
will be visited very often. The debugging infrastructure is guarded
under a static_key, which is global.