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

Liam R. Howlett
2026-02-12T18:31:27Z

* 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