linux-kernel - Re: [PATCH] mm, THP: vmf_insert_pfn_pud depends on CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE

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Date:   Thu, 11 Jan 2018 11:06:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Alexandre Ghiti <aghiti@...em.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, dan.j.williams@...el.com,
        zi.yan@...rutgers.edu, gregkh@...uxfoundation.org,
        n-horiguchi@...jp.nec.com, willy@...ux.intel.com,
        mark.rutland@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, THP: vmf_insert_pfn_pud depends on
 CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD

On Thu 11-01-18 09:53:31, Alexandre Ghiti wrote:
> The only definition of vmf_insert_pfn_pud depends on
> CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD being defined. Then its declaration in
> include/linux/huge_mm.h should have the same restriction so that we do
> not expose this function if CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD is
> not defined.

Why is this a problem? Compiler should simply throw away any
declarations which are not used?

> Signed-off-by: Alexandre Ghiti <aghiti@...em.com>
> ---
>  include/linux/huge_mm.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index a8a1262..11794f6a 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -48,8 +48,10 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  			int prot_numa);
>  int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  			pmd_t *pmd, pfn_t pfn, bool write);
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>  int vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
>  			pud_t *pud, pfn_t pfn, bool write);
> +#endif
>  enum transparent_hugepage_flag {
>  	TRANSPARENT_HUGEPAGE_FLAG,
>  	TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> -- 
> 2.1.4
> 

-- 
Michal Hocko
SUSE Labs