linux-kernel - Re: [PATCH -mm] mm, madvise, THP: Use THP aligned address in madvise_free_huge

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Date:   Wed, 14 Mar 2018 21:39:54 -0400
From:   "Zi Yan" <zi.yan@...rutgers.edu>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     "Andrew Morton" <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Michal Hocko" <mhocko@...e.com>,
        "Minchan Kim" <minchan@...nel.org>, "Shaohua Li" <shli@...nel.org>,
        jglisse@...hat.com,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH -mm] mm, madvise, THP: Use THP aligned address in
 madvise_free_huge_pmd()

This cannot happen.

Two address parameters are passed: addr and next.
If “addr” is not aligned and “next” is aligned or the end of madvise range, which might not be aligned,
either way next - addr < HPAGE_PMD_SIZE.

This means the code in “if (next - addr != HPAGE_PMD_SIZE)”, which is above your second hunk,
will split the THP between “addr” and “next” and get out as long as “addr“ is not aligned.
Thus, the code in your second hunk should always get aligned “addr”.

Let me know if I miss anything.

—
Best Regards,
Yan Zi

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

> From: Huang Ying <ying.huang@...el.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@...el.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Shaohua Li <shli@...nel.org>
> Cc: Zi Yan <zi.yan@...rutgers.edu>
> Cc: jglisse@...hat.com
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.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 = tlb->mm;
>  	bool ret = false;
> +	unsigned long haddr = 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 *tlb, 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 = pmd_mkold(orig_pmd);
>  		orig_pmd = 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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