linux-kernel - Re: [RFC PATCH 3/8] [NET]: uninline dev_alloc

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Message-ID: <47BC54FB.2050508@trash.net>
Date:	Wed, 20 Feb 2008 17:27:39 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
CC:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC PATCH 3/8] [NET]: uninline dev_alloc_skb, de-bloats a lot

Jan Engelhardt wrote:
> On Feb 20 2008 15:47, Ilpo Järvinen wrote:
>> -23668  392 funcs, 104 +, 23772 -, diff: -23668 --- dev_alloc_skb
>>
>> -static inline struct sk_buff *dev_alloc_skb(unsigned int length)
>> -{
>> -	return __dev_alloc_skb(length, GFP_ATOMIC);
>> -}
>> +extern struct sk_buff *dev_alloc_skb(unsigned int length);
> 
> Striking. How can this even happen? A callsite which calls
> 
> 	dev_alloc_skb(n)
> 
> is just equivalent to
> 
> 	__dev_alloc_skb(n, GFP_ATOMIC);
> 
> which means there's like 4 (or 8 if it's long) bytes more on the
> stack. For a worst case, count in another 8 bytes for push and pop or mov on
> the stack. But that still does not add up to 23 kb.


__dev_alloc_skb() is also an inline function which performs
some extra work. Which raises the question - if dev_alloc_skb()
is uninlined, shouldn't __dev_alloc_skb() be uninline as well?
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