linux-kernel - Re: [PATCH 1/3] resources: introduce generic page_is

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Date:	Fri, 22 Jan 2010 13:52:17 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Xiaotian Feng <xtfeng@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chen Liqin <liqin.chen@...plusct.com>,
	Lennox Wu <lennox.wu@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yinghai Lu <yinghai@...nel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Zheng, Shaohui" <shaohui.zheng@...el.com>
Subject: Re: [PATCH 1/3] resources: introduce generic page_is_ram()

On Thu, Jan 21, 2010 at 09:50:01PM -0800, Xiaotian Feng wrote:
> On Fri, Jan 22, 2010 at 1:37 PM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> > On Thu, Jan 21, 2010 at 10:15:50PM -0700, Xiaotian Feng wrote:
> >> On Fri, Jan 22, 2010 at 11:21 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> >> > It's based on walk_system_ram_range(), for archs that don't have
> >> > their own page_is_ram().
> >> >
> >> > The static verions in MIPS and SCORE are also made global.
> >> >
> >> > CC: Chen Liqin <liqin.chen@...plusct.com>
> >> > CC: Lennox Wu <lennox.wu@...il.com>
> >> > CC: Ralf Baechle <ralf@...ux-mips.org>
> >> > CC: Américo Wang <xiyou.wangcong@...il.com>
> >> > CC: linux-mips@...ux-mips.org
> >> > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >> > CC: Yinghai Lu <yinghai@...nel.org>
> >> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> >> > ---
> >> >  arch/mips/mm/init.c    |    2 +-
> >> >  arch/score/mm/init.c   |    2 +-
> >> >  include/linux/ioport.h |    2 ++
> >> >  kernel/resource.c      |   11 +++++++++++
> >> >  4 files changed, 15 insertions(+), 2 deletions(-)
> >> >
> >> > --- linux-mm.orig/kernel/resource.c     2010-01-22 11:20:34.000000000 +0800
> >> > +++ linux-mm/kernel/resource.c  2010-01-22 11:20:35.000000000 +0800
> >> > @@ -327,6 +327,17 @@ int walk_system_ram_range(unsigned long
> >> >
> >> >  #endif
> >> >
> >> > +#define PAGE_IS_RAM    24
> >> > +static int __is_ram(unsigned long pfn, unsigned long nr_pages, void *arg)
> >> > +{
> >> > +       return PAGE_IS_RAM;
> >> > +}
> >> > +int __attribute__((weak)) page_is_ram(unsigned long pfn)
> >> > +{
> >> > +       return PAGE_IS_RAM == walk_system_ram_range(pfn, 1, NULL, __is_ram);
> >> > +}
> >> > +#undef PAGE_IS_RAM
> >> > +
> >>
> >> I'm not sure, but any build test for powerpc/mips/score?
> >
> > Sorry, no build tests yet:
> >
> >        /bin/sh: score-linux-gcc: command not found
> >
> > I just make the mips/score page_is_ram() non-static and assume that
> > will make it compile.
> >
> >> walk_system_ram_range is defined when CONFIG_ARCH_HAS_WALK_MEMORY is not set.
> >> Is it safe when CONFIG_ARCH_HAS_WALK_MEMORY is set for some powerpc archs?
> >
> > Good question. Grep shows that CONFIG_ARCH_HAS_WALK_MEMORY is only
> > defined for powerpc, and it has its own page_is_ram() as well as
> > walk_system_ram_range().
> >
> > walk_system_ram_range() must be defined somewhere because it is
> > expected to be generic routine: exported and called from both
> > in-kernel and out-of-tree code.
> >
> 
> Yes, powerpc has its own walk_system_ram_range() and page_is_ram() ;-)
> 
> Would it be better if moving the weak attribute page_is_ram() into #if
> !defined(CONFIG_ARCH_HAS_WALK_MEMORY) ?

Only several archs defined page_is_ram(), so that would not be feasible
for doing a _generic_ page_is_ram().

Thanks,
Fengguang
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