netdev - Re: [PATCH net-next 3/6] tcp_metrics: Add a field tcpm

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Date:	Tue, 10 Mar 2015 10:23:12 +0200 (EET)
From:	Julian Anastasov <ja@....bg>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	David Miller <davem@...emloft.net>, edumazet@...gle.com,
	netdev@...r.kernel.org, stephen@...workplumber.org,
	nicolas.dichtel@...nd.com, roopa@...ulusnetworks.com,
	hannes@...essinduktion.org, ddutt@...ulusnetworks.com,
	vipin@...ulusnetworks.com, shmulik.ladkani@...il.com,
	dsahern@...il.com
Subject: Re: [PATCH net-next 3/6] tcp_metrics: Add a field tcpm_net and verify
 it matches on lookup


	Hello,

On Tue, 10 Mar 2015, Eric W. Biederman wrote:

> Julian Anastasov <ja@....bg> writes:
> 
> >>  struct tcp_metrics_block {
> >>  	struct tcp_metrics_block __rcu	*tcpm_next;
> >> +	struct net			*tcpm_net;
> >
> > 	Is it better if we have this field under
> > #ifef CONFIG_NET_NS ? read_pnet and write_pnet do not
> > care when first argument is not declared for the
> > !CONFIG_NET_NS case.
> 
> I don't actually believe there are many people compiling out network
> namespaces but there is no point in making it unnecessarily bad for them.

	Small routers. Also, we can move tcpm_net after
tcpm_daddr to help machines with 32-byte cache line.
It would be good if fields and access is in this order:
tcpm_next, tcpm_daddr, tcpm_saddr and finally tcpm_net.
tcpm_daddr is the leading key, it was tcpm_addr originally.
If such change is not suitable for this patchset I can try it
later after your changes.

> That said.  If we actually really care about struct net going away it
> would be much better to globally replace struct net with a typedef that
> looks something like:
> 
> #ifdef CONFIG_NET_NS
> struct net_ref {
>        struct net *;
> };
> #else
> struct net_ref {
> };
> #endif
> typedef struct net_ref net_t;
> 
> That would remove the need for write_pnet and read_pnet, make it
> impossible to forget net_eq and make network namespace arguments to
> functions also boil away at compile time if the network namespace code
> was not enabled.
> 
> That was the original design and I forget why we didn't do that with
> struct net.  But we did not.

	Not sure. Only macros help to avoid ifdefs here
and there in the code...

> In this specific case an extra member of tcp_metrics_block isn't going
> to hurt so I don't think write_pnet and read_pnet are particularly
> interesting.   net_eq definitely seems worthwhile.

	Lets use them, even neighbour.c uses them.
Your patchset shows the direction we go, net field to be
part of the structures and using common tables.
Macros like write_pnet and read_pnet look the only
way to save memory on small systems. And net_eq should
be optimized by compilers too.

Regards

--
Julian Anastasov <ja@....bg>
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