Re: [PATCH v3 1/4] mm: don't special case !MMU for is_zero_pfn() and my_zero_pfn()

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Mike Rapoport <rppt@kernel.org> [260211 05:32]:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> nommu architectures have empty_zero_page and define ZERO_PAGE() and
> although they don't really use it to populate page tables, there is no
> reason to hardwire !MMU implementation of is_zero_pfn() and my_zero_pfn()
> to 0.
> 
> Drop #ifdef CONFIG_MMU around implementations of is_zero_pfn() and
> my_zero_pfn() and remove !MMU version.
> 
> While on it, make zero_pfn __ro_after_init.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  include/linux/pgtable.h | 14 +-------------
>  mm/memory.c             | 13 -------------
>  mm/mm_init.c            | 10 ++++++++++
>  3 files changed, 11 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 827dca25c0bc..08a88b0d56e5 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1882,7 +1882,6 @@ static inline void pfnmap_setup_cachemode_pfn(unsigned long pfn, pgprot_t *prot)
>  	pfnmap_setup_cachemode(pfn, PAGE_SIZE, prot);
>  }
>  
> -#ifdef CONFIG_MMU
>  #ifdef __HAVE_COLOR_ZERO_PAGE
>  static inline int is_zero_pfn(unsigned long pfn)
>  {
> @@ -1905,18 +1904,7 @@ static inline unsigned long my_zero_pfn(unsigned long addr)
>  	extern unsigned long zero_pfn;
>  	return zero_pfn;
>  }
> -#endif
> -#else
> -static inline int is_zero_pfn(unsigned long pfn)
> -{
> -	return 0;
> -}
> -
> -static inline unsigned long my_zero_pfn(unsigned long addr)
> -{
> -	return 0;
> -}
> -#endif /* CONFIG_MMU */
> +#endif /* __HAVE_COLOR_ZERO_PAGE */
>  
>  #ifdef CONFIG_MMU
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 187f16b7e996..51d2018a387a 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -162,21 +162,8 @@ static int __init disable_randmaps(char *s)
>  }
>  __setup("norandmaps", disable_randmaps);
>  
> -unsigned long zero_pfn __read_mostly;
> -EXPORT_SYMBOL(zero_pfn);
> -
>  unsigned long highest_memmap_pfn __read_mostly;
>  
> -/*
> - * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
> - */
> -static int __init init_zero_pfn(void)
> -{
> -	zero_pfn = page_to_pfn(ZERO_PAGE(0));
> -	return 0;
> -}
> -early_initcall(init_zero_pfn);
> -
>  void mm_trace_rss_stat(struct mm_struct *mm, int member)
>  {
>  	trace_rss_stat(mm, member);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 1a29a719af58..dcf9eff34f83 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -53,6 +53,9 @@ EXPORT_SYMBOL(mem_map);
>  void *high_memory;
>  EXPORT_SYMBOL(high_memory);
>  
> +unsigned long zero_pfn __ro_after_init;
> +EXPORT_SYMBOL(zero_pfn);
> +
>  #ifdef CONFIG_DEBUG_MEMORY_INIT
>  int __meminitdata mminit_loglevel;
>  
> @@ -2667,6 +2670,13 @@ static void __init mem_init_print_info(void)
>  		);
>  }
>  
> +static int __init init_zero_pfn(void)
> +{
> +	zero_pfn = page_to_pfn(ZERO_PAGE(0));
> +	return 0;
> +}
> +early_initcall(init_zero_pfn);
> +
>  void __init __weak arch_mm_preinit(void)
>  {
>  }
> -- 
> 2.51.0
>