linux-kernel - Re: [RFC 3/6] mm: support madvise(MADV

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Message-ID: <20140314133311.GA6316@node.dhcp.inet.fi>
Date:	Fri, 14 Mar 2014 15:33:11 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	John Stultz <john.stultz@...aro.org>, Jason Evans <je@...com>
Subject: Re: [RFC 3/6] mm: support madvise(MADV_FREE)

On Fri, Mar 14, 2014 at 03:37:47PM +0900, Minchan Kim wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c1b7414c7bef..9b048cabce27 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -933,10 +933,16 @@ void page_address_init(void);
>   * Please note that, confusingly, "page_mapping" refers to the inode
>   * address_space which maps the page from disk; whereas "page_mapped"
>   * refers to user virtual address space into which the page is mapped.
> + *
> + * PAGE_MAPPING_LZFREE bit is set along with PAGE_MAPPING_ANON bit
> + * and then page->mapping points to an anon_vma. This flag is used
> + * for lazy freeing the page instead of swap.
>   */
>  #define PAGE_MAPPING_ANON	1
>  #define PAGE_MAPPING_KSM	2
> -#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
> +#define PAGE_MAPPING_LZFREE	4
> +#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM | \
> +				 PAGE_MAPPING_LZFREE)

Is it safe to use third bit in pointer everywhere?

-- 
 Kirill A. Shutemov
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