netdev - Re: [PATCH net-next v2 0/5] net: skbuff: hide some bitfield members

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Date:   Mon, 17 Apr 2023 12:26:16 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com
Subject: Re: [PATCH net-next v2 0/5] net: skbuff: hide some bitfield members

On Mon, 17 Apr 2023 08:53:45 -0700 Jakub Kicinski wrote:
> There is a number of protocol or subsystem specific fields
> in struct sk_buff which are only accessed by one subsystem.
> We can wrap them in ifdefs with minimal code impact.
> 
> This gives us a better chance to save a 2B and a 4B holes
> resulting with the following savings (assuming a lucky
> kernel config):
> 
> -	/* size: 232, cachelines: 4, members: 28 */
> -	/* sum members: 227, holes: 1, sum holes: 4 */
> -	/* sum bitfield members: 8 bits (1 bytes) */
> +	/* size: 224, cachelines: 4, members: 28 */
>  	/* forced alignments: 2 */
> -	/* last cacheline: 40 bytes */
> +	/* last cacheline: 32 bytes */
> 
> I think that the changes shouldn't be too controversial.
> The only one I'm not 100% sure of is the SCTP one,
> 12 extra LoC for one bit.. But it did fit squarely
> in the "this bit has only one user" category.

Missed Simon's tag, sorry about that: 
https://lore.kernel.org/all/ZD03APYJqdhflYNJ@kernel.org/

Acked-by: Simon Horman <horms@...nel.org>