linux-kernel - Re: [PATCH 1/1] page_alloc.c: remove argument to pageblock_default

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Date:	Thu, 10 May 2012 14:34:55 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	rajman mekaco <rajman.mekaco@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Minchan Kim <minchan.kim@...il.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH 1/1] page_alloc.c: remove argument to
 pageblock_default_order

On Thu, May 03, 2012 at 04:37:49PM -0700, Andrew Morton wrote:
> On Thu,  3 May 2012 22:45:12 +0530
> rajman mekaco <rajman.mekaco@...il.com> wrote:
> 
> > When CONFIG_HUGETLB_PAGE_SIZE_VARIABLE is not defined, then
> > pageblock_default_order has an argument to it.
> > 
> > However, free_area_init_core will call it without any argument
> > anyway.
> > 
> > Remove the argument to pageblock_default_order when
> > CONFIG_HUGETLB_PAGE_SIZE_VARIABLE is not defined.
> > 
> > Signed-off-by: rajman mekaco <rajman.mekaco@...il.com>
> > ---
> >  mm/page_alloc.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index a712fb9..4b95412 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4274,7 +4274,7 @@ static inline void __init set_pageblock_order(unsigned int order)
> >   * at compile-time. See include/linux/pageblock-flags.h for the values of
> >   * pageblock_order based on the kernel config
> >   */
> > -static inline int pageblock_default_order(unsigned int order)
> > +static inline int pageblock_default_order(void)
> >  {
> >  	return MAX_ORDER-1;
> >  }
> 
> Interesting.  It has been that way since at least 3.1.
> 

/me slaps self

> It didn't break the build because pageblock_default_order() is only
> ever invoked by set_pageblock_order(), with:
> 
> 	set_pageblock_order(pageblock_default_order());
> 
> and set_pageblock_order() is a macro:
> 
> #define set_pageblock_order(x)	do {} while (0)
> 
> There's yet another reason not to use macros, dammit - they hide bugs.
> 
> 
> Mel, can you have a think about this please?  Can we just kill off
> pageblock_default_order() and fold its guts into
> set_pageblock_order(void)?  Only ia64 and powerpc can define
> CONFIG_HUGETLB_PAGE_SIZE_VARIABLE.
> 

This looks reasonable to me.

-- 
Mel Gorman
SUSE Labs
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