Re: [PATCH nf-next 1/2] netfilter: move nat hlist_head to nf_conn

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, Jul 05, 2016 at 12:07:23PM +0200, Florian Westphal wrote:
> The nat extension structure is 32bytes in size on x86_64:
> 
> struct nf_conn_nat {
>         struct hlist_node          bysource;             /*     0    16 */
>         struct nf_conn *           ct;                   /*    16     8 */
>         union nf_conntrack_nat_help help;                /*    24     4 */
>         int                        masq_index;           /*    28     4 */
>         /* size: 32, cachelines: 1, members: 4 */
>         /* last cacheline: 32 bytes */
> };
> 
> The hlist is needed to quickly check for possible tuple collisions
> when installing a new nat binding. Storing this in the extension
> area has two drawbacks:
> 
> 1. We need ct backpointer to get the conntrack struct from the extension.
> 2. When reallocation of extension area occurs we need to fixup the bysource
>    hash head via hlist_replace_rcu.
> 
> We can avoid both by placing the hlist_head in nf_conn and place nf_conn in
> the bysource hash rather than the extenstion.
> 
> We can also remove the ->move support; no other extension needs it.
> 
> Moving the entire nat extension into nf_conn would be possible as well but
> then we have to add yet another callback for deletion from the bysource
> hash table rather than just using nat extension ->destroy hook for this.
> 
> nf_conn size doesn't increase due to aligment, followup patch replaces
> hlist_node with single pointer.

Applied, thanks.