Re: [PATCH v3 4/4] mm: cache struct page for empty_zero_page and return it from ZERO_PAGE()

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

* Mike Rapoport <rppt@kernel.org> [260211 05:32]:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> For most architectures every invocation of ZERO_PAGE() does
> virt_to_page(empty_zero_page). But empty_zero_page is in BSS and it is
> enough to get its struct page once at initialization time and then use
> it whenever a zero page should be accessed.
> 
> Add yet another __zero_page variable that will be initialized as
> virt_to_page(empty_zero_page) for most architectures in a weak
> arch_setup_zero_pages() function.
> 
> For architectures that use colored zero pages (MIPS and s390) rename their
> setup_zero_pages() to arch_setup_zero_pages() and make it global rather
> than static.
> 
> For architectures that cannot use virt_to_page() for BSS (arm64 and
> sparc64) add override of arch_setup_zero_pages().
> 
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

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

> ---
>  arch/arm64/include/asm/pgtable.h    |  6 ------
>  arch/arm64/mm/init.c                |  5 +++++
>  arch/mips/mm/init.c                 | 11 +----------
>  arch/s390/mm/init.c                 |  4 +---
>  arch/sparc/include/asm/pgtable_64.h |  3 ---
>  arch/sparc/mm/init_64.c             | 17 +++++++----------
>  include/linux/pgtable.h             | 11 ++++++++---
>  mm/mm_init.c                        | 21 +++++++++++++++++----
>  8 files changed, 39 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 63da07398a30..2c1ec7cc8612 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -106,12 +106,6 @@ static inline void arch_leave_lazy_mmu_mode(void)
>  #define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp)	\
>  	local_flush_tlb_page_nonotify(vma, address)
>  
> -/*
> - * ZERO_PAGE is a global shared page that is always zero: used
> - * for zero-mapped memory areas etc..
> - */
> -#define ZERO_PAGE(vaddr)	phys_to_page(__pa_symbol(empty_zero_page))
> -
>  #define pte_ERROR(e)	\
>  	pr_err("%s:%d: bad pte %016llx.\n", __FILE__, __LINE__, pte_val(e))
>  
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 96711b8578fd..417ec7efe569 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -328,6 +328,11 @@ void __init bootmem_init(void)
>  	memblock_dump_all();
>  }
>  
> +void __init arch_setup_zero_pages(void)
> +{
> +	__zero_page = phys_to_page(__pa_symbol(empty_zero_page));
> +}
> +
>  void __init arch_mm_preinit(void)
>  {
>  	unsigned int flags = SWIOTLB_VERBOSE;
> diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
> index 4f6449ad02ca..55b25e85122a 100644
> --- a/arch/mips/mm/init.c
> +++ b/arch/mips/mm/init.c
> @@ -56,10 +56,7 @@ unsigned long empty_zero_page, zero_page_mask;
>  EXPORT_SYMBOL_GPL(empty_zero_page);
>  EXPORT_SYMBOL(zero_page_mask);
>  
> -/*
> - * Not static inline because used by IP27 special magic initialization code
> - */
> -static void __init setup_zero_pages(void)
> +void __init arch_setup_zero_pages(void)
>  {
>  	unsigned int order;
>  
> @@ -450,7 +447,6 @@ void __init arch_mm_preinit(void)
>  	BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (PFN_PTE_SHIFT > PAGE_SHIFT));
>  
>  	maar_init();
> -	setup_zero_pages();	/* Setup zeroed pages.  */
>  	highmem_init();
>  
>  #ifdef CONFIG_64BIT
> @@ -461,11 +457,6 @@ void __init arch_mm_preinit(void)
>  				0x80000000 - 4, KCORE_TEXT);
>  #endif
>  }
> -#else  /* CONFIG_NUMA */
> -void __init arch_mm_preinit(void)
> -{
> -	setup_zero_pages();	/* This comes from node 0 */
> -}
>  #endif /* !CONFIG_NUMA */
>  
>  void free_init_pages(const char *what, unsigned long begin, unsigned long end)
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 3c20475cbee2..1f72efc2a579 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -69,7 +69,7 @@ unsigned long empty_zero_page, zero_page_mask;
>  EXPORT_SYMBOL(empty_zero_page);
>  EXPORT_SYMBOL(zero_page_mask);
>  
> -static void __init setup_zero_pages(void)
> +void __init arch_setup_zero_pages(void)
>  {
>  	unsigned long total_pages = memblock_estimated_nr_free_pages();
>  	unsigned int order;
> @@ -159,8 +159,6 @@ void __init arch_mm_preinit(void)
>  	cpumask_set_cpu(0, mm_cpumask(&init_mm));
>  
>  	pv_init();
> -
> -	setup_zero_pages();	/* Setup zeroed pages. */
>  }
>  
>  unsigned long memory_block_size_bytes(void)
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 615f460c50af..74ede706fb32 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -210,9 +210,6 @@ extern unsigned long _PAGE_CACHE;
>  extern unsigned long pg_iobits;
>  extern unsigned long _PAGE_ALL_SZ_BITS;
>  
> -extern struct page *mem_map_zero;
> -#define ZERO_PAGE(vaddr)	(mem_map_zero)
> -
>  /* PFNs are real physical page numbers.  However, mem_map only begins to record
>   * per-page information starting at pfn_base.  This is to handle systems where
>   * the first physical page in the machine is at some huge physical address,
> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> index 0cc8de2fea90..707c1df67d79 100644
> --- a/arch/sparc/mm/init_64.c
> +++ b/arch/sparc/mm/init_64.c
> @@ -177,9 +177,6 @@ extern unsigned long sparc_ramdisk_image64;
>  extern unsigned int sparc_ramdisk_image;
>  extern unsigned int sparc_ramdisk_size;
>  
> -struct page *mem_map_zero __read_mostly;
> -EXPORT_SYMBOL(mem_map_zero);
> -
>  unsigned int sparc64_highest_unlocked_tlb_ent __read_mostly;
>  
>  unsigned long sparc64_kern_pri_context __read_mostly;
> @@ -2496,11 +2493,17 @@ static void __init register_page_bootmem_info(void)
>  			register_page_bootmem_info_node(NODE_DATA(i));
>  #endif
>  }
> -void __init mem_init(void)
> +
> +void __init arch_setup_zero_pages(void)
>  {
>  	phys_addr_t zero_page_pa = kern_base +
>  		((unsigned long)&empty_zero_page[0] - KERNBASE);
>  
> +	__zero_page = phys_to_page(zero_page_pa);
> +}
> +
> +void __init mem_init(void)
> +{
>  	/*
>  	 * Must be done after boot memory is put on freelist, because here we
>  	 * might set fields in deferred struct pages that have not yet been
> @@ -2509,12 +2512,6 @@ void __init mem_init(void)
>  	 */
>  	register_page_bootmem_info();
>  
> -	/*
> -	 * Set up the zero page, mark it reserved, so that page count
> -	 * is not manipulated when freeing the page from user ptes.
> -	 */
> -	mem_map_zero = pfn_to_page(PHYS_PFN(zero_page_pa));
> -
>  	if (tlb_type == cheetah || tlb_type == cheetah_plus)
>  		cheetah_ecache_flush_init();
>  }
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 3d48eea57cd2..1da21ec62836 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1894,6 +1894,8 @@ static inline void pfnmap_setup_cachemode_pfn(unsigned long pfn, pgprot_t *prot)
>   * For architectures that don't __HAVE_COLOR_ZERO_PAGE the zero page lives in
>   * empty_zero_page in BSS.
>   */
> +void arch_setup_zero_pages(void);
> +
>  #ifdef __HAVE_COLOR_ZERO_PAGE
>  static inline int is_zero_pfn(unsigned long pfn)
>  {
> @@ -1921,10 +1923,13 @@ static inline unsigned long zero_pfn(unsigned long addr)
>  }
>  
>  extern uint8_t empty_zero_page[PAGE_SIZE];
> +extern struct page *__zero_page;
>  
> -#ifndef ZERO_PAGE
> -#define ZERO_PAGE(vaddr) ((void)(vaddr),virt_to_page(empty_zero_page))
> -#endif
> +static inline struct page *_zero_page(unsigned long addr)
> +{
> +	return __zero_page;
> +}
> +#define ZERO_PAGE(vaddr) _zero_page(vaddr)
>  
>  #endif /* __HAVE_COLOR_ZERO_PAGE */
>  
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 1eac634ece1a..b08608c1b71d 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -59,7 +59,10 @@ EXPORT_SYMBOL(zero_page_pfn);
>  #ifndef __HAVE_COLOR_ZERO_PAGE
>  uint8_t empty_zero_page[PAGE_SIZE] __page_aligned_bss;
>  EXPORT_SYMBOL(empty_zero_page);
> -#endif
> +
> +struct page *__zero_page __ro_after_init;
> +EXPORT_SYMBOL(__zero_page);
> +#endif /* __HAVE_COLOR_ZERO_PAGE */
>  
>  #ifdef CONFIG_DEBUG_MEMORY_INIT
>  int __meminitdata mminit_loglevel;
> @@ -2675,12 +2678,21 @@ static void __init mem_init_print_info(void)
>  		);
>  }
>  
> -static int __init init_zero_page_pfn(void)
> +#ifndef __HAVE_COLOR_ZERO_PAGE
> +/*
> + * architectures that __HAVE_COLOR_ZERO_PAGE must define this function
> + */
> +void __init __weak arch_setup_zero_pages(void)
> +{
> +	__zero_page = virt_to_page(empty_zero_page);
> +}
> +#endif
> +
> +static void __init init_zero_page_pfn(void)
>  {
> +	arch_setup_zero_pages();
>  	zero_page_pfn = page_to_pfn(ZERO_PAGE(0));
> -	return 0;
>  }
> -early_initcall(init_zero_page_pfn);
>  
>  void __init __weak arch_mm_preinit(void)
>  {
> @@ -2704,6 +2716,7 @@ void __init mm_core_init_early(void)
>  void __init mm_core_init(void)
>  {
>  	arch_mm_preinit();
> +	init_zero_page_pfn();
>  
>  	/* Initializations relying on SMP setup */
>  	BUILD_BUG_ON(MAX_ZONELISTS > 2);
> -- 
> 2.51.0
>