Re: [PATCH 04 of 30] clear compound mapping

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Thu, 2010-01-21 at 07:20 +0100, Andrea Arcangeli wrote:
> Clear compound mapping for anonymous compound pages like it already happens for
> regular anonymous pages.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -584,6 +584,8 @@ static void __free_pages_ok(struct page 
> 
>  	kmemcheck_free_shadow(page, order);
> 
> +	if (PageAnon(page))
> +		page->mapping = NULL;
>  	for (i = 0 ; i < (1 << order) ; ++i)
>  		bad += free_pages_check(page + i);
>  	if (bad)

This one may at least need a bit of an enhanced patch description.  I
didn't immediately remember that __free_pages_ok() is only actually
called for compound pages.

Would it make more sense to pull the page->mapping=NULL out of
free_hot_cold_page(), and just put a single one in __free_pages()?

I guess we'd also need one in free_compound_page() since it calls
__free_pages_ok() directly.  But, if this patch were putting modifying
free_compound_page() it would at least be super obvious what was going
on.

-- Dave

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