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Date: Wed, 16 Sep 2015 15:25:40 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>,
        "Matthew Wilcox" <matthew.r.wilcox@intel.com>,
        Minchan Kim <minchan@kernel.org>, <linux-arch@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <arc-linux-dev@synopsys.com>
Subject: Re: [PATCH 08/11] mm,thp: reduce ifdef'ery for THP in generic code
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On Thu, 27 Aug 2015 14:33:11 +0530 Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:

> This is purely cosmetic, just makes code more readable
> 
> ...
>
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -30,9 +30,20 @@ extern int ptep_set_access_flags(struct vm_area_struct *vma,
>  #endif
>  
>  #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  extern int pmdp_set_access_flags(struct vm_area_struct *vma,
>  				 unsigned long address, pmd_t *pmdp,
>  				 pmd_t entry, int dirty);
> +#else /* CONFIG_TRANSPARENT_HUGEPAGE */
> +static inline int pmdp_set_access_flags(struct vm_area_struct *vma,
> +					unsigned long address, pmd_t *pmdp,
> +					pmd_t entry, int dirty)
> +{
> +	BUG();
> +	return 0;
> +}

Is it possible to simply leave this undefined?  So the kernel fails at
link time?

> --- a/mm/pgtable-generic.c
> +++ b/mm/pgtable-generic.c

Good heavens that file is a mess.  Your patch does improve it.