linux-kernel - Re: [PATCH 1/6] mm: define PAGE_MAPPING

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Message-ID: <4B049090.1070300@redhat.com>
Date:	Wed, 18 Nov 2009 19:25:52 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/6] mm: define PAGE_MAPPING_FLAGS

On 11/10/2009 04:51 PM, Hugh Dickins wrote:
> At present we define PageAnon(page) by the low PAGE_MAPPING_ANON bit
> set in page->mapping, with the higher bits a pointer to the anon_vma;
> and have defined PageKsm(page) as that with NULL anon_vma.
>
> But KSM swapping will need to store a pointer there: so in preparation
> for that, now define PAGE_MAPPING_FLAGS as the low two bits, including
> PAGE_MAPPING_KSM (always set along with PAGE_MAPPING_ANON, until some
> other use for the bit emerges).
>
> Declare page_rmapping(page) to return the pointer part of page->mapping,
> and page_anon_vma(page) to return the anon_vma pointer when that's what
> it is.  Use these in a few appropriate places: notably, unuse_vma() has
> been testing page->mapping, but is better to be testing page_anon_vma()
> (cases may be added in which flag bits are set without any pointer).
>
> Signed-off-by: Hugh Dickins<hugh.dickins@...cali.co.uk>
>
>    
Reviewed-by: Rik van Riel <riel@...hat.com>

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