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From:   "Zi Yan" <zi.yan@cs.rutgers.edu>
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     "Andrew Morton" <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Michal Hocko" <mhocko@suse.com>,
        "Minchan Kim" <minchan@kernel.org>, "Shaohua Li" <shli@kernel.org>,
        jglisse@redhat.com,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH -mm] mm, madvise, THP: Use THP aligned address in
 madvise_free_huge_pmd()
Date:   Wed, 14 Mar 2018 21:39:54 -0400
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This cannot happen.

Two address parameters are passed: addr and next.
If =E2=80=9Caddr=E2=80=9D is not aligned and =E2=80=9Cnext=E2=80=9D is al=
igned or the end of madvise range, which might not be aligned,
either way next - addr < HPAGE_PMD_SIZE.

This means the code in =E2=80=9Cif (next - addr !=3D HPAGE_PMD_SIZE)=E2=80=
=9D, which is above your second hunk,
will split the THP between =E2=80=9Caddr=E2=80=9D and =E2=80=9Cnext=E2=80=
=9D and get out as long as =E2=80=9Caddr=E2=80=9C is not aligned.
Thus, the code in your second hunk should always get aligned =E2=80=9Cadd=
r=E2=80=9D.

Let me know if I miss anything.

=E2=80=94
Best Regards,
Yan Zi

On 14 Mar 2018, at 21:18, Huang, Ying wrote:

> From: Huang Ying <ying.huang@intel.com>
>
> The address argument passed in madvise_free_huge_pmd() may be not THP
> aligned.  But some THP operations like pmdp_invalidate(),
> set_pmd_at(), and tlb_remove_pmd_tlb_entry() need the address to be
> THP aligned.  Fix this via using THP aligned address for these
> functions in madvise_free_huge_pmd().
>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Shaohua Li <shli@kernel.org>
> Cc: Zi Yan <zi.yan@cs.rutgers.edu>
> Cc: jglisse@redhat.com
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  mm/huge_memory.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0cc62405de9c..c5e1bfb08bd7 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1617,6 +1617,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb=
, struct vm_area_struct *vma,
>  	struct page *page;
>  	struct mm_struct *mm =3D tlb->mm;
>  	bool ret =3D false;
> +	unsigned long haddr =3D addr & HPAGE_PMD_MASK;
>
>  	tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
>
> @@ -1663,12 +1664,12 @@ bool madvise_free_huge_pmd(struct mmu_gather *t=
lb, struct vm_area_struct *vma,
>  	unlock_page(page);
>
>  	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
> -		pmdp_invalidate(vma, addr, pmd);
> +		pmdp_invalidate(vma, haddr, pmd);
>  		orig_pmd =3D pmd_mkold(orig_pmd);
>  		orig_pmd =3D pmd_mkclean(orig_pmd);
>
> -		set_pmd_at(mm, addr, pmd, orig_pmd);
> -		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> +		set_pmd_at(mm, haddr, pmd, orig_pmd);
> +		tlb_remove_pmd_tlb_entry(tlb, pmd, haddr);
>  	}
>
>  	mark_page_lazyfree(page);
> -- =

> 2.16.1

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