[PATCH 1/3 v4] resources: introduce generic page_is_ram()

Wu Fengguang
2010-01-22T08:16:27Z

On Fri, Jan 22, 2010 at 12:51:32AM -0700, H. Peter Anvin wrote:
> On 01/21/2010 07:21 PM, Wu Fengguang wrote:
> > --- 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
> > +
>
> Stylistic nitpick:
>
> The use of the magic number "24" here is pretty ugly; it seems to imply
> that there is something peculiar with this number and that it is trying
> to avoid an overlap, whereas in fact any number but 0 and -1 would do.

Yes, exactly.

> I would rather see just returning 1 and do:
>
> return walk_system_ram_range(pfn, 1, NULL, __is_ram) == 1;
>
> (walk_system_ram_range() returning -1 on error, and 0 means continue.)

Good suggestion.

> Note also that we don't write "constant == expression"; although some
> schools teach it as a way to avoid the "=" versus "==" beginner C
> mistake, it makes the code less intuitive to read.

Yeah.

> Other than that, the patchset looks good; if Ingo doesn't beat me to it
> I'll put it in tomorrow (need sleep right now.)

OK, thanks! Here is the updated patch.

---
resources: introduce generic page_is_ram()

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.

v4: prefer plain 1 instead of PAGE_IS_RAM (H. Peter Anvin)
v3: add comment (KAMEZAWA Hiroyuki)
"AFAIK, this "System RAM" information has been used for kdump to
grab valid memory area and seems good for the kernel itself."
v2: add PAGE_IS_RAM macro (Américo Wang)

CC: Chen Liqin <liqin.chen@sunplusct.com>
CC: Lennox Wu <lennox.wu@gmail.com>
CC: Ralf Baechle <ralf@linux-mips.org>
CC: Américo Wang <xiyou.wangcong@gmail.com>
CC: linux-mips@linux-mips.org
CC: Yinghai Lu <yinghai@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
arch/mips/mm/init.c | 2 +-
arch/score/mm/init.c | 2 +-
include/linux/ioport.h | 2 ++
kernel/resource.c | 13 +++++++++++++
4 files changed, 17 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 16:12:55.000000000 +0800
@@ -327,6 +327,19 @@ int walk_system_ram_range(unsigned long

#endif

+static int __is_ram(unsigned long pfn, unsigned long nr_pages, void *arg)
+{
+ return 1;
+}
+/*
+ * This generic page_is_ram() returns true if specified address is
+ * registered as "System RAM" in iomem_resource list.
+ */
+int __attribute__((weak)) page_is_ram(unsigned long pfn)
+{
+ return walk_system_ram_range(pfn, 1, NULL, __is_ram) == 1;
+}
+
/*
* Find empty slot in the resource tree given range and alignment.
*/
--- linux-mm.orig/include/linux/ioport.h 2010-01-22 11:20:34.000000000 +0800
+++ linux-mm/include/linux/ioport.h 2010-01-22 11:20:35.000000000 +0800
@@ -191,5 +191,7 @@ extern int
walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
void *arg, int (*func)(unsigned long, unsigned long, void *));

+extern int page_is_ram(unsigned long pfn);
+
#endif /* __ASSEMBLY__ */
#endif /* _LINUX_IOPORT_H */
--- linux-mm.orig/arch/score/mm/init.c 2010-01-22 11:20:34.000000000 +0800
+++ linux-mm/arch/score/mm/init.c 2010-01-22 11:20:35.000000000 +0800
@@ -59,7 +59,7 @@ static unsigned long setup_zero_page(voi
}

#ifndef CONFIG_NEED_MULTIPLE_NODES
-static int __init page_is_ram(unsigned long pagenr)
+int page_is_ram(unsigned long pagenr)
{
if (pagenr >= min_low_pfn && pagenr < max_low_pfn)
return 1;
--- linux-mm.orig/arch/mips/mm/init.c 2010-01-22 11:20:34.000000000 +0800
+++ linux-mm/arch/mips/mm/init.c 2010-01-22 11:20:35.000000000 +0800
@@ -298,7 +298,7 @@ void __init fixrange_init(unsigned long
}

#ifndef CONFIG_NEED_MULTIPLE_NODES
-static int __init page_is_ram(unsigned long pagenr)
+int page_is_ram(unsigned long pagenr)
{
int i;