Re: [PATCH 1/6] mm: define PAGE_MAPPING_FLAGS

[Rik van Riel <riel@redhat.com>]

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@tiscali.co.uk>
>
>    
Reviewed-by: Rik van Riel <riel@redhat.com>