linux-kernel - Re: [PATCH] rmap: Fix compound check logic in page_remove_file

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Date:	Tue, 9 Aug 2016 19:29:15 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Steve Capper <steve.capper@....com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	shijie.huang@....com, will.deacon@....com, catalin.marinas@....com
Subject: Re: [PATCH] rmap: Fix compound check logic in page_remove_file_rmap

On Tue, Aug 09, 2016 at 01:34:35PM +0100, Steve Capper wrote:
> In page_remove_file_rmap(.) we have the following check:
>   VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> 
> This is meant to check for either HugeTLB pages or THP when a compound
> page is passed in.
> 
> Unfortunately, if one disables CONFIG_TRANSPARENT_HUGEPAGE, then
> PageTransHuge(.) will always return false provoking BUGs when one runs
> the libhugetlbfs test suite.
> 
> Changing the definition of PageTransHuge to be defined for
> !CONFIG_TRANSPARENT_HUGEPAGE turned out to provoke build bugs; so this
> patch instead replaces the errant check with:
>   PageTransHuge(page) || PageHuge(page)

I think PageHead() check should be enough to cover this.

> 
> Fixes: dd78fedde4b9 ("rmap: support file thp")
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Steve Capper <steve.capper@....com>
> ---
>  mm/rmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 709bc83..ad8fc51 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1303,7 +1303,7 @@ static void page_remove_file_rmap(struct page *page, bool compound)
>  {
>  	int i, nr = 1;
>  
> -	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
> +	VM_BUG_ON_PAGE(compound && !(PageTransHuge(page) || PageHuge(page)), page);
>  	lock_page_memcg(page);
>  
>  	/* Hugepages are not counted in NR_FILE_MAPPED for now. */
> -- 
> 1.8.3.1
> 
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-- 
 Kirill A. Shutemov