linux-kernel - Re: [PATCH] rmap: fix pgoff calculation to handle hugepage correctly

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Message-ID: <20140701180739.GA4985@node.dhcp.inet.fi>
Date:	Tue, 1 Jul 2014 21:07:39 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH] rmap: fix pgoff calculation to handle hugepage correctly

On Tue, Jul 01, 2014 at 10:46:22AM -0400, Naoya Horiguchi wrote:
> I triggered VM_BUG_ON() in vma_address() when I try to migrate an anonymous
> hugepage with mbind() in the kernel v3.16-rc3. This is because pgoff's
> calculation in rmap_walk_anon() fails to consider compound_order() only to
> have an incorrect value. So this patch fixes it.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
>  mm/rmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git v3.16-rc3.orig/mm/rmap.c v3.16-rc3/mm/rmap.c
> index b7e94ebbd09e..8cc964c6bd8d 100644
> --- v3.16-rc3.orig/mm/rmap.c
> +++ v3.16-rc3/mm/rmap.c
> @@ -1639,7 +1639,7 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page,
>  static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
>  {
>  	struct anon_vma *anon_vma;
> -	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
> +	pgoff_t pgoff = page->index << compound_order(page);
>  	struct anon_vma_chain *avc;
>  	int ret = SWAP_AGAIN;

Hm. It will not work with THP: ->index there is in PAGE_SIZE units.

Why do we need this special case for hugetlb page ->index? Why not use
PAGE_SIZE units there too? Or I miss something?

-- 
 Kirill A. Shutemov
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