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

Kirill A. Shutemov
2014-07-01T18:08:07Z

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@ah.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