[PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[Wang Sheng-Hui]

Per the void prep_compound_page(struct page *page, unsigned long order) code,
compound pages use PG_head/PG_tail, and only tail pages point at head page
using their ->first_page field.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
---
 mm/page_alloc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e8ecb6..f645ce8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -332,8 +332,8 @@ out:
  *
  * The remaining PAGE_SIZE pages are called "tail pages".
  *
- * All pages have PG_compound set.  All pages have their ->private pointing at
- * the head page (even the head page has this).
+ * Head page has PG_head set, and all tail pages have PG_tail set. All tail
+ * pages have their ->first_page pointing at the head page.
  *
  * The first tail page's ->lru.next holds the address of the compound page's
  * put_page() function.  Its ->lru.prev holds the order of allocation.
-- 
1.7.1

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Re: [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[Michal Hocko]

On Tue 15-11-11 16:06:16, Wang Sheng-Hui wrote:
> Per the void prep_compound_page(struct page *page, unsigned long order) code,
> compound pages use PG_head/PG_tail, 

This is true only for CONFIG_PAGEFLAGS_EXTENDED otherwise we trick it by
PG_compound & ~PG_reclaim = head page
PG_compound & PG_reclaim = tail page

Have a look at PG_head_tail_mask

> and only tail pages point at head page using their ->first_page field.

This part is correct.

> 
> Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
> ---
>  mm/page_alloc.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6e8ecb6..f645ce8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -332,8 +332,8 @@ out:
>   *
>   * The remaining PAGE_SIZE pages are called "tail pages".
>   *
> - * All pages have PG_compound set.  All pages have their ->private pointing at
> - * the head page (even the head page has this).
> + * Head page has PG_head set, and all tail pages have PG_tail set. All tail
> + * pages have their ->first_page pointing at the head page.
>   *
>   * The first tail page's ->lru.next holds the address of the compound page's
>   * put_page() function.  Its ->lru.prev holds the order of allocation.
> -- 
> 1.7.1
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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Re: [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[Wang Sheng-Hui]

On 2011a1'11ae??15ae?JPY 21:24, Michal Hocko wrote:
> On Tue 15-11-11 16:06:16, Wang Sheng-Hui wrote:
>> Per the void prep_compound_page(struct page *page, unsigned long order) code,
>> compound pages use PG_head/PG_tail, 
> 
> This is true only for CONFIG_PAGEFLAGS_EXTENDED otherwise we trick it by
> PG_compound & ~PG_reclaim = head page
> PG_compound & PG_reclaim = tail page
> 
> Have a look at PG_head_tail_mask
> 
>> and only tail pages point at head page using their ->first_page field.
> 
> This part is correct.
> 
>>
>> Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
>> ---
>>  mm/page_alloc.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 6e8ecb6..f645ce8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -332,8 +332,8 @@ out:
>>   *
>>   * The remaining PAGE_SIZE pages are called "tail pages".
>>   *
>> - * All pages have PG_compound set.  All pages have their ->private pointing at
>> - * the head page (even the head page has this).
>> + * Head page has PG_head set, and all tail pages have PG_tail set. All tail
>> + * pages have their ->first_page pointing at the head page.
>>   *
>>   * The first tail page's ->lru.next holds the address of the compound page's
>>   * put_page() function.  Its ->lru.prev holds the order of allocation.
>> -- 
>> 1.7.1
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 

Thanks, Michal.

New patch generated.


[PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

Only tail pages point at the head page using their ->first_page fields.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
---
 mm/page_alloc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e8ecb6..e7dd848 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -332,8 +332,8 @@ out:
  *
  * The remaining PAGE_SIZE pages are called "tail pages".
  *
- * All pages have PG_compound set.  All pages have their ->private pointing at
- * the head page (even the head page has this).
+ * All pages have PG_compound set.  All tail pages have their ->first_page
+ * pointing at the head page.
  *
  * The first tail page's ->lru.next holds the address of the compound page's
  * put_page() function.  Its ->lru.prev holds the order of allocation.
-- 
1.7.1


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Re: [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[Michal Hocko]

[CCing trivial tree]

Unquoted patch at https://lkml.org/lkml/2011/11/15/402

On Wed 16-11-11 08:05:07, Wang Sheng-Hui wrote:
[...]
> Thanks, Michal.
> 
> New patch generated.
> 
> 
> [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c
> 
> Only tail pages point at the head page using their ->first_page fields.
> 
> Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/page_alloc.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6e8ecb6..e7dd848 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -332,8 +332,8 @@ out:
>   *
>   * The remaining PAGE_SIZE pages are called "tail pages".
>   *
> - * All pages have PG_compound set.  All pages have their ->private pointing at
> - * the head page (even the head page has this).
> + * All pages have PG_compound set.  All tail pages have their ->first_page
> + * pointing at the head page.
>   *
>   * The first tail page's ->lru.next holds the address of the compound page's
>   * put_page() function.  Its ->lru.prev holds the order of allocation.
> -- 
> 1.7.1

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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Re: [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c

[Jiri Kosina]

On Thu, 17 Nov 2011, Michal Hocko wrote:

> [CCing trivial tree]
> 
> Unquoted patch at https://lkml.org/lkml/2011/11/15/402
> 
> On Wed 16-11-11 08:05:07, Wang Sheng-Hui wrote:
> [...]
> > Thanks, Michal.
> > 
> > New patch generated.
> > 
> > 
> > [PATCH] mm: cleanup the comment for head/tail pages of compound pages in mm/page_alloc.c
> > 
> > Only tail pages point at the head page using their ->first_page fields.
> > 
> > Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
> 
> Reviewed-by: Michal Hocko <mhocko@suse.cz>

Applied, thanks.

-- 
Jiri Kosina
SUSE Labs

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