Re: [B.A.T.M.A.N.] [RFC] batman-adv: Reorder structs to reduce padding

On Monday 05 November 2012 19:58:54 Marek Lindner wrote:

On Sunday, November 04, 2012 06:41:48 Sven Eckelmann wrote:

...

•   struct batadv_neigh_node __rcu *router; /* rcu protected pointer
  

*/

#ifdef CONFIG_BATMAN_ADV_DAT

    batadv_dat_addr_t dat_addr;

#endif

•   uint8_t flags;
  

•   uint8_t gw_flags;
  

•   struct batadv_neigh_node __rcu *router; /* rcu protected pointer
  

*/

Shouldn't we move batadv_dat_addr_t to the end of the struct to achieve the smallest possible struct regardless of whether DAT is compiled in or not ? Or does it have no effect ?

More or less. It is hard to optimize it for both situation. Just moving to the end will not fix the problem because it will create an 1 byte whole which has to filled using something else. And optimizing it for all architectures is even harder.

But this RFC is not really important. It was just a small fun test of pahole for me.

Kind regards, Sven