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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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