linux-kernel - Re: [PATCH v3 4/6] mm/hugetlb: Allow architectures to override huge_pte

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Date:   Mon, 22 May 2017 15:59:43 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Punit Agrawal <punit.agrawal@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, n-horiguchi@...jp.nec.com,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        mike.kravetz@...cle.com, steve.capper@....com,
        Mark Rutland <mark.rutland@....com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 4/6] mm/hugetlb: Allow architectures to override huge_pte_clear()

On Mon, May 22, 2017 at 3:36 PM, Punit Agrawal <punit.agrawal@....com> wrote:
> diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
> index 99b490b4d05a..3138e126f43b 100644
> --- a/include/asm-generic/hugetlb.h
> +++ b/include/asm-generic/hugetlb.h
> @@ -31,10 +31,7 @@ static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
>         return pte_modify(pte, newprot);
>  }
>
> -static inline void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
> -                                 pte_t *ptep)
> -{
> -       pte_clear(mm, addr, ptep);
> -}
> +void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
> +                   pte_t *ptep, unsigned long sz);
>
>  #endif /* _ASM_GENERIC_HUGETLB_H */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0e4d1fb3122f..2b0f6f96f2c1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3289,6 +3289,12 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
>         return ret;
>  }
>
> +void __weak huge_pte_clear(struct mm_struct *mm, unsigned long addr,
> +                          pte_t *ptep, unsigned long sz)
> +{
> +       pte_clear(mm, addr, ptep);
> +}
> +
>  void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
>                             unsigned long start, unsigned long end,
>                             struct page *ref_page)

I don't really like how this moves the inline version from asm-generic into
a __weak function here. I think it would be better to either stop
using asm-generic/hugetlb.h
on s390, or enclose the generic definition in

#ifndef huge_pte_clear

and then override by defining a macro in s390 as we do in other files
in asm-generic.

       Arnd