netdev - Re: [PATCH net-next 0/1 v2] skbuff: Extend gso

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Date:   Sun, 9 Apr 2017 19:07:24 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     steffen.klassert@...unet.com
Cc:     edumazet@...gle.com, davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/1 v2] skbuff: Extend gso_type to unsigned int.

>  struct skb_shared_info {
> +	unsigned short	_unused;
>  	unsigned char	nr_frags;

This makes _all_ fields to be accessed with offset, but if you move
padding down, at least ->nr_frags will enjoy clean and simple [R64]
addressing.

On allyesconfig-ish kernel:

	before:	+542 = 720-178
	 after:	-158 =  53-211 (negative, because 16-bit field became 32-bit)

You may want to add configurable redzone there instead of padding
if that what you want. 2 bytes is nothing.