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Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race

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On Mon, Mar 06, 2017 at 08:19:03AM +0530, Aneesh Kumar K.V wrote:
> "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:
> 
> > Basically the same race as with numa balancing in change_huge_pmd(), but
> > a bit simpler to mitigate: we don't need to preserve dirty/young flags
> > here due to MADV_FREE functionality.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Cc: Minchan Kim <minchan@kernel.org>
> > ---
> >  mm/huge_memory.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index bb2b3646bd78..324217c31ec9 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1566,8 +1566,6 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> >  		deactivate_page(page);
> >  
> >  	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
> > -		orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
> > -			tlb->fullmm);
> >  		orig_pmd = pmd_mkold(orig_pmd);
> >  		orig_pmd = pmd_mkclean(orig_pmd);
> >  
> 
> Instead can we do a new interface that does something like
> 
> pmdp_huge_update(tlb->mm, addr, pmd, new_pmd);
> 
> We do have a variant already in ptep_set_access_flags. What we need is
> something that can be used to update THP pmd, without converting it to
> pmd_none and one which doens't loose reference and change bit ?

Sounds like a good idea. Would you volunteer to implement it?
I don't have time for this right now.

-- 
 Kirill A. Shutemov

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[PATCH 0/4] thp: fix few MADV_DONTNEED races "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-02 16:20 +0100
  [PATCH 4/4] thp: fix MADV_DONTNEED vs clear soft dirty race "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-02 17:00 +0100
    Re: [PATCH 4/4] thp: fix MADV_DONTNEED vs clear soft dirty race Andrew Morton <akpm@linux-foundation.org> - 2017-03-03 23:50 +0100
  [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-02 17:00 +0100
    Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2017-03-03 06:40 +0100
      Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-03 11:30 +0100
        Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race Minchan Kim <minchan@kernel.org> - 2017-03-06 03:00 +0100
          Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-07 15:40 +0100
    Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-03-06 03:50 +0100
      Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-07 15:50 +0100
  [PATCH 1/4] thp: reduce indentation level in change_huge_pmd() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-02 17:00 +0100
  [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-03-03 03:20 +0100
    Re: [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race Dave Hansen <dave.hansen@intel.com> - 2017-03-03 18:20 +0100

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