The field page->flags is defined as unsigned long and is divided into
several parts to store different information of the page, like section,
node, zone. Which means all parts must sit in the one "unsigned
long".
BITS_PER_LONG is used in several places to ensure this applies.
#if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
While we use "sizeof(unsigned long) * 8" in the definition of
SECTIONS_PGOFF
#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
This may not be that obvious for audience to catch the point.
This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to
make all this consistent.
Signed-off-by: Wei Yang <[email protected]>
---
include/linux/mm.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b84615b0f64c..a5d80de089ff 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -684,7 +684,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf);
*/
/* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_CPUPID] | ... | FLAGS | */
-#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
+#define SECTIONS_PGOFF (BITS_PER_LONG - SECTIONS_WIDTH)
#define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH)
#define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH)
#define LAST_CPUPID_PGOFF (ZONES_PGOFF - LAST_CPUPID_WIDTH)
--
2.11.0
On Sat 18-03-17 08:39:14, Wei Yang wrote:
> The field page->flags is defined as unsigned long and is divided into
> several parts to store different information of the page, like section,
> node, zone. Which means all parts must sit in the one "unsigned
> long".
>
> BITS_PER_LONG is used in several places to ensure this applies.
>
> #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>
> While we use "sizeof(unsigned long) * 8" in the definition of
> SECTIONS_PGOFF
>
> #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
>
> This may not be that obvious for audience to catch the point.
>
> This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to
> make all this consistent.
I am not really sure this is an improvement. page::flags is unsigned
long nad the current code reflects that type.
> Signed-off-by: Wei Yang <[email protected]>
> ---
> include/linux/mm.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b84615b0f64c..a5d80de089ff 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -684,7 +684,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf);
> */
>
> /* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_CPUPID] | ... | FLAGS | */
> -#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
> +#define SECTIONS_PGOFF (BITS_PER_LONG - SECTIONS_WIDTH)
> #define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH)
> #define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH)
> #define LAST_CPUPID_PGOFF (ZONES_PGOFF - LAST_CPUPID_WIDTH)
> --
> 2.11.0
>
--
Michal Hocko
SUSE Labs
On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote:
>On Sat 18-03-17 08:39:14, Wei Yang wrote:
>> The field page->flags is defined as unsigned long and is divided into
>> several parts to store different information of the page, like section,
>> node, zone. Which means all parts must sit in the one "unsigned
>> long".
>>
>> BITS_PER_LONG is used in several places to ensure this applies.
>>
>> #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
>> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>>
>> While we use "sizeof(unsigned long) * 8" in the definition of
>> SECTIONS_PGOFF
>>
>> #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
>>
>> This may not be that obvious for audience to catch the point.
>>
>> This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to
>> make all this consistent.
>
>I am not really sure this is an improvement. page::flags is unsigned
>long nad the current code reflects that type.
>
Hi, Michal
Glad to hear from you.
I think the purpose of definition BITS_PER_LONG is more easily to let audience
know it is the number of bits of type long. If it has no improvement, we don't
need to define a specific macro .
And as you could see, several related macros use BITS_PER_LONG in their
definition. After this change, all of them will have a consistent definition.
After this change, code looks more neat :-)
So it looks more reasonable to use this.
--
Wei Yang
Help you, Help me
On Sun 19-03-17 23:03:45, Wei Yang wrote:
> On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote:
> >On Sat 18-03-17 08:39:14, Wei Yang wrote:
> >> The field page->flags is defined as unsigned long and is divided into
> >> several parts to store different information of the page, like section,
> >> node, zone. Which means all parts must sit in the one "unsigned
> >> long".
> >>
> >> BITS_PER_LONG is used in several places to ensure this applies.
> >>
> >> #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
> >> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
> >> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
> >>
> >> While we use "sizeof(unsigned long) * 8" in the definition of
> >> SECTIONS_PGOFF
> >>
> >> #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
> >>
> >> This may not be that obvious for audience to catch the point.
> >>
> >> This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to
> >> make all this consistent.
> >
> >I am not really sure this is an improvement. page::flags is unsigned
> >long nad the current code reflects that type.
> >
>
> Hi, Michal
>
> Glad to hear from you.
>
> I think the purpose of definition BITS_PER_LONG is more easily to let audience
> know it is the number of bits of type long. If it has no improvement, we don't
> need to define a specific macro .
>
> And as you could see, several related macros use BITS_PER_LONG in their
> definition. After this change, all of them will have a consistent definition.
>
> After this change, code looks more neat :-)
>
> So it looks more reasonable to use this.
I do not think that this is sufficient to justify the change.
--
Michal Hocko
SUSE Labs
On Sun, Mar 19, 2017 at 11:08:22AM -0400, Michal Hocko wrote:
>On Sun 19-03-17 23:03:45, Wei Yang wrote:
>> On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote:
>> >On Sat 18-03-17 08:39:14, Wei Yang wrote:
>> >> The field page->flags is defined as unsigned long and is divided into
>> >> several parts to store different information of the page, like section,
>> >> node, zone. Which means all parts must sit in the one "unsigned
>> >> long".
>> >>
>> >> BITS_PER_LONG is used in several places to ensure this applies.
>> >>
>> >> #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
>> >> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>> >> #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>> >>
>> >> While we use "sizeof(unsigned long) * 8" in the definition of
>> >> SECTIONS_PGOFF
>> >>
>> >> #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - SECTIONS_WIDTH)
>> >>
>> >> This may not be that obvious for audience to catch the point.
>> >>
>> >> This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to
>> >> make all this consistent.
>> >
>> >I am not really sure this is an improvement. page::flags is unsigned
>> >long nad the current code reflects that type.
>> >
>>
>> Hi, Michal
>>
>> Glad to hear from you.
>>
>> I think the purpose of definition BITS_PER_LONG is more easily to let audience
>> know it is the number of bits of type long. If it has no improvement, we don't
>> need to define a specific macro .
>>
>> And as you could see, several related macros use BITS_PER_LONG in their
>> definition. After this change, all of them will have a consistent definition.
>>
>> After this change, code looks more neat :-)
>>
>> So it looks more reasonable to use this.
>
>I do not think that this is sufficient to justify the change.
>
Fine~ Thanks for comments~
>--
>Michal Hocko
>SUSE Labs
--
Wei Yang
Help you, Help me