linux-kernel - Re: [PATCH 1/1] mm: unify pmd

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Message-ID: <488DF119.2000004@gmail.com>
Date:	Mon, 28 Jul 2008 18:17:29 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: unify pmd_free() implementation

Linus Torvalds wrote:
> 
> On Mon, 28 Jul 2008, Andrea Righi wrote:
>> Move multiple definitions of pmd_free() from different include/asm-* into
>> mm/util.c.
> 
> But this is horrible, because it forces a totally unnecessary function 
> call for that empty function.
> 
> Yeah, the function will be cheap, but the call itself will not be (it's a 
> C language barrier and basically disables optimizations around it, causing 
> thigns like register spill/reload for no good reason).
> 
> 		Linus

yep! clear.

Ok, in this case wouldn't be better at least to define pud_free() as:

static inline pud_free(struct mm_struct *mm, pmd_t *pmd)
{
}

in include/asm-generic/pgtable-nopmd.h, just to avoid the warning
on x86 without PAE?

Thanks for the explanation,
-Andrea
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