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    SubjectRe: [patch] hugetlb: correct page offset index for sharing pmd
    On Mon 13-08-12 20:10:41, Hillf Danton wrote:
    > 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?

    That one is surely correct (linear_page_index converts the page offset).
    Anyway do you actually have any _real_ objection to the patch? I think
    the generated discussion is not worth the whole discussion.

    > > 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

    --
    Michal Hocko
    SUSE Labs


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