linux-kernel - Re: [PATCH] mm/pgtable: Move extern zero_pfn outside __HAVE_COLOR_ZERO

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Message-ID: <f55dff2d-d32e-8de1-0177-e6ba713e0cd9@redhat.com>
Date:   Tue, 16 Jun 2020 09:39:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/pgtable: Move extern zero_pfn outside
 __HAVE_COLOR_ZERO_PAGE

On 16.06.20 06:08, Anshuman Khandual wrote:
> zero_pfn variable is required whether __HAVE_COLOR_ZERO_PAGE is enabled

Why is that relevant for this patch?

> or not. Also it should not really be declared individually in all functions
> where it gets used. Just move the declaration outside, which also makes it
> available for other potential users.

So, all you're essentially doing is exposing zero_pfn in pgtable.h now.

If everybody should just use my_zero_pfn(), I don't really see the
benefit of this patch, sorry.

> 
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: linux-arch@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Applies on 5.8-rc1. If the earlier motivation was to hide zero_pfn from
> general visibility, we could just put in a comment and update the commit
> message that my_zero_pfn() should always be used rather than zero_pfn.
> Build tested on many platforms and boot tested on arm64, x86.
> 
>  include/linux/pgtable.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 32b6c52d41b9..078e9864abca 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1020,10 +1020,11 @@ extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
>  extern void untrack_pfn_moved(struct vm_area_struct *vma);
>  #endif
>  
> +extern unsigned long zero_pfn;
> +
>  #ifdef __HAVE_COLOR_ZERO_PAGE
>  static inline int is_zero_pfn(unsigned long pfn)
>  {
> -	extern unsigned long zero_pfn;
>  	unsigned long offset_from_zero_pfn = pfn - zero_pfn;
>  	return offset_from_zero_pfn <= (zero_page_mask >> PAGE_SHIFT);
>  }
> @@ -1033,13 +1034,11 @@ static inline int is_zero_pfn(unsigned long pfn)
>  #else
>  static inline int is_zero_pfn(unsigned long pfn)
>  {
> -	extern unsigned long zero_pfn;
>  	return pfn == zero_pfn;
>  }
>  
>  static inline unsigned long my_zero_pfn(unsigned long addr)
>  {
> -	extern unsigned long zero_pfn;
>  	return zero_pfn;
>  }
>  #endif
> 


-- 
Thanks,

David / dhildenb