[PATCH v2 08/10] Add page_is_buddy for PG_buddy

[Atsushi Kumagai]

Hello HATAYAMA-san,

On Fri, 16 Nov 2012 14:02:13 +0900
HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote:

> On kernels from v2.6.18 to v2.6.37, buddy page is marked by the
> PG_buddy flag.
> 
>   kernel version     | PG_buddy
>   ------------------ +---------------------------------
>   v2.6.17 to v2.6.26 | 19
>   v2.6.27 to v2.6.37 | 19 if CONFIG_PAGEFLAGS_EXTEND=y
>                      | 18 otherwise
> 
> We don't need to care about CONFIG_PAGEFLAGS_EXTEND because the
> architectures specifying this as y are um and xtensa only. They are
> not included in the supported architectures of makedumpfile.

Sorry for too late point out.

I did regression test for v1.5.1 on x86_64 machine in the last weekend
and found the issue that page_is_buddy_v2() can't exclude free pages
correctly for kernel 2.6.30 to 2.6.37. 
I checked the configuration of these kernels, I made sure that
CONFIG_PAGEFLAGS_EXTENDED was set as y, so PG_buddy=18 is invalid for them.

According to this fact, PG_buddy is variable for the supported architectures
of makedumpfile, too.
So, how did you confirm that CONFIG_PAGEFLAGS_EXTENDED is only related with
um and xtensa ?

And why did you test with PG_buddy=19 for 2.6.32 when you posted this patch set?

>  - 2.6.32
>  NUMBER(PG_slab)=7
>  NUMBER(PG_buddy)=19
>  OFFSET(page._mapcount)=12
>  OFFSET(page.private)=16
>  SIZE(pageflags)=4


Thanks
Atsushi Kumagai
 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
> ---
> 
>  makedumpfile.c |   24 ++++++++++++++++++++----
>  1 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 7b13dca..4e5d4d3 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -3669,6 +3669,19 @@ exclude_free_page(void)
>  }
>  
>  /*
> + * For the kernel versions from v2.6.17 to v2.6.37.
> + */
> +static int
> +page_is_buddy_v2(unsigned long flags, unsigned int _mapcount,
> +			unsigned long private, unsigned int _count)
> +{
> +	if (flags & (1UL << NUMBER(PG_buddy)))
> +		return TRUE;
> +
> +	return FALSE;
> +}
> +
> +/*
>   * For v2.6.38 and later kernel versions.
>   */
>  static int
> @@ -3690,10 +3703,13 @@ setup_page_is_buddy(void)
>  	if (OFFSET(page.private) == NOT_FOUND_STRUCTURE)
>  		goto out;
>  
> -	if (NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) != NOT_FOUND_NUMBER) {
> -		if (OFFSET(page._mapcount) != NOT_FOUND_STRUCTURE)
> -			info->page_is_buddy = page_is_buddy_v3;
> -	}
> +	if (NUMBER(PG_buddy) == NOT_FOUND_NUMBER) {
> +		if (NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) != NOT_FOUND_NUMBER) {
> +			if (OFFSET(page._mapcount) != NOT_FOUND_STRUCTURE)
> +				info->page_is_buddy = page_is_buddy_v3;
> +		}
> +	} else
> +		info->page_is_buddy = page_is_buddy_v2;
>  
>  out:
>  	if (!info->page_is_buddy)
> 
> 
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