linux-kernel - Re: [PATCH 2/2] mm: Fixup abandoned PG

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Date:	Fri, 28 Sep 2012 12:34:25 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Li Haifeng <omycle@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: Fixup abandoned PG_buddy for private in struct
 page

On Thu, Sep 06, 2012 at 05:11:18PM +0800, Li Haifeng wrote:
> PG_buddy, an abandoned flag, indicates page(s) is/are free
> and in buddy allocator. And when page(s) in buddy allocator,
> the _mapcount will equal PAGE_BUDDY_MAPCOUNT_VALUE. So,
> here, "_mapcount equals PAGE_BUDDY_MAPCOUNT_VALUE" instead
> of "PG_buddy is set".
> 
> Signed-off-by: Haifeng Li <omycle@...il.com>
> ---
>  include/linux/mm_types.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 704a626..49d9247 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -126,7 +126,8 @@ struct page {
>                                                  * if PagePrivate set; used for
>                                                  * swp_entry_t if PageSwapCache;
>                                                  * indicates order in the buddy
> -                                                * system if PG_buddy is set.
> +                                                * system if _mapcount equals
> +                                                * PAGE_BUDDY_MAPCOUNT_VALUE.

How about simply "if PageBuddy", just like the previous sentence about
swap cache does?  No reason to expose the implementation of PageBuddy
at this point, I guess...
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