Re: [patch] hugetlb: correct page offset index for sharing pmd

[Hillf Danton <dhillf@gmail.com>]

On Sun, Aug 12, 2012 at 5:31 PM, Michal Hocko <mhocko@suse.cz> wrote:
> From d07b88a70ee1dbcc96502c48cde878931e7deb38 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.cz>
> Date: Fri, 10 Aug 2012 15:03:07 +0200
> Subject: [PATCH] hugetlb: do not use vma_hugecache_offset for
>  vma_prio_tree_foreach
>
> 0c176d5 (mm: hugetlb: fix pgoff computation when unmapping page
> from vma) fixed pgoff calculation but it has replaced it by
> vma_hugecache_offset which is not approapriate for offsets used for
> vma_prio_tree_foreach because that one expects index in page units
> rather than in huge_page_shift.


What if another case of vma_prio_tree_foreach in try_to_unmap_file
is correct?


> Using vma_hugecache_offset is not incorrect because the pgoff will fit
> into the same vmas but it is confusing so the standard PAGE_SHIFT based
> index calculation is used instead.
>
> Cc: Hillf Danton <dhillf@gmail.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
> ---
>  mm/hugetlb.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c39e4be..a74ea31 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2462,7 +2462,8 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
>          * from page cache lookup which is in HPAGE_SIZE units.
>          */
>         address = address & huge_page_mask(h);
> -       pgoff = vma_hugecache_offset(h, vma, address);
> +       pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
> +                       vma->vm_pgoff;
>         mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
>
>         /*
> --
> 1.7.10.4
>
>
> --
> Michal Hocko
> SUSE Labs

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