linux-kernel - Re: [PATCH] netns: deinline net

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Date:	Tue, 14 Apr 2015 06:19:32 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Jiri Pirko <jpirko@...hat.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] netns: deinline net_generic()

On Tue, 2015-04-14 at 14:25 +0200, Denys Vlasenko wrote:
> On x86 allyesconfig build:
> The function compiles to 130 bytes of machine code.
> It has 493 callsites.
> Total reduction of vmlinux size: 27906 bytes.
> 
>    text	     data      bss       dec     hex filename
> 82447071 22255384 20627456 125329911 77861f7 vmlinux4
> 82419165 22255384 20627456 125302005 777f4f5 vmlinux5

This sounds a big hammer to me.

These savings probably comes from the BUG_ON() that could simply be
removed.
The second one for sure has no purpose. First one looks defensive.

For a typical (non allyesconfig) kernel, net_generic() would translate
to :

return net->gen[id - 1]


Tunnels need this in fast path, so I presume we could introduce
net_generic_rcu() to keep this stuff inlined where it matters.

static inline void *net_generic_rcu(const struct net *net, int id)
{
	struct net_generic *ng = rcu_dereference(net->gen);

	return ng->ptr[id - 1];
}



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