netdev - Re: [PATCH v2 1/2] sctp: compress bit-wide flags to a bitfield on sctp

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Message-ID: <1459972404.6715.65.camel@perches.com>
Date:	Wed, 06 Apr 2016 12:53:24 -0700
From:	Joe Perches <joe@...ches.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	netdev@...r.kernel.org
Cc:	Neil Horman <nhorman@...driver.com>,
	Vlad Yasevich <vyasevich@...il.com>, linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sctp: compress bit-wide flags to a bitfield on
 sctp_sock

On Wed, 2016-04-06 at 14:53 -0300, Marcelo Ricardo Leitner wrote:
> It wastes space and gets worse as we add new flags, so convert bit-wide
> flags to a bitfield.
> 
> Currently it already saves 4 bytes in sctp_sock, which are left as holes
> in it for now. The whole struct needs packing, which should be done in
> another patch.
> 
> Note that do_auto_asconf cannot be merged, as explained in the comment
> before it.
> 
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
[]
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
[]
> @@ -210,14 +210,14 @@ struct sctp_sock {
>  	int user_frag;
>  
>  	__u32 autoclose;
> -	__u8 nodelay;
> -	__u8 disable_fragments;
> -	__u8 v4mapped;
> -	__u8 frag_interleave;
>  	__u32 adaptation_ind;
>  	__u32 pd_point;
> -	__u8 recvrcvinfo;
> -	__u8 recvnxtinfo;
> +	__u16	nodelay:1,
> +		disable_fragments:1,
> +		v4mapped:1,
> +		frag_interleave:1,
> +		recvrcvinfo:1,
> +		recvnxtinfo:1;

Might as well make this __u32 as the next field would be
aligned on an atomic_t

It might be better if these fields didn't use the __ prefix.