Re: [PATCH] mm: Remove misleading ARCH_USES_NUMA_PROT_NONE

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Mel Gorman <mgorman@suse.de> writes:

> ARCH_USES_NUMA_PROT_NONE was defined for architectures that implemented
> _PAGE_NUMA using _PROT_NONE. This saved using an additional PTE bit and
> relied on the fact that PROT_NONE vmas were skipped by the NUMA hinting
> fault scanner. This was found to be conceptually confusing with a lot of
> implicit assumptions and it was asked that an alternative be found.
>
> Commit c46a7c81 "x86: define _PAGE_NUMA by reusing software bits on the
> PMD and PTE levels" redefined _PAGE_NUMA on x86 to be one of the swap
> PTE bits and shrunk the maximum possible swap size but it did not go far
> enough. There are no architectures that reuse _PROT_NONE as _PROT_NUMA
> but the relics still exist.
>
> This patch removes ARCH_USES_NUMA_PROT_NONE and removes some unnecessary
> duplication in powerpc vs the generic implementation by defining the types
> the core NUMA helpers expected to exist from x86 with their ppc64 equivalent.
> This necessitated that a PTE bit mask be created that identified the bits
> that distinguish present from NUMA pte entries but it is expected this
> will only differ between arches based on _PAGE_PROTNONE. The naming for
> the generic helpers was taken from x86 originally but ppc64 has types that
> are equivalent for the purposes of the helper so they are mapped instead
> of duplicating code.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>  arch/powerpc/include/asm/pgtable.h    | 57 ++++++++---------------------------
>  arch/powerpc/include/asm/pte-common.h |  5 +++
>  arch/x86/Kconfig                      |  1 -
>  arch/x86/include/asm/pgtable_types.h  | 14 +++++++++
>  include/asm-generic/pgtable.h         | 27 ++++++-----------
>  init/Kconfig                          | 11 -------
>  6 files changed, 40 insertions(+), 75 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index d98c1ec..f60d4ea 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -38,10 +38,9 @@ static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK)
>  static inline pgprot_t pte_pgprot(pte_t pte)	{ return __pgprot(pte_val(pte) & PAGE_PROT_BITS); }
>  
>  #ifdef CONFIG_NUMA_BALANCING
> -
>  static inline int pte_present(pte_t pte)
>  {
> -	return pte_val(pte) & (_PAGE_PRESENT | _PAGE_NUMA);
> +	return pte_val(pte) & _PAGE_NUMA_MASK;
>  }
>  
>  #define pte_present_nonuma pte_present_nonuma
> @@ -50,37 +49,6 @@ static inline int pte_present_nonuma(pte_t pte)
>  	return pte_val(pte) & (_PAGE_PRESENT);
>  }
>  
> -#define pte_numa pte_numa
> -static inline int pte_numa(pte_t pte)
> -{
> -	return (pte_val(pte) &
> -		(_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA;
> -}
> -
> -#define pte_mknonnuma pte_mknonnuma
> -static inline pte_t pte_mknonnuma(pte_t pte)
> -{
> -	pte_val(pte) &= ~_PAGE_NUMA;
> -	pte_val(pte) |=  _PAGE_PRESENT | _PAGE_ACCESSED;
> -	return pte;
> -}
> -
> -#define pte_mknuma pte_mknuma
> -static inline pte_t pte_mknuma(pte_t pte)
> -{
> -	/*
> -	 * We should not set _PAGE_NUMA on non present ptes. Also clear the
> -	 * present bit so that hash_page will return 1 and we collect this
> -	 * as numa fault.
> -	 */
> -	if (pte_present(pte)) {
> -		pte_val(pte) |= _PAGE_NUMA;
> -		pte_val(pte) &= ~_PAGE_PRESENT;
> -	} else
> -		VM_BUG_ON(1);
> -	return pte;
> -}
> -
>  #define ptep_set_numa ptep_set_numa
>  static inline void ptep_set_numa(struct mm_struct *mm, unsigned long addr,
>  				 pte_t *ptep)
> @@ -92,12 +60,6 @@ static inline void ptep_set_numa(struct mm_struct *mm, unsigned long addr,
>  	return;
>  }
>  
> -#define pmd_numa pmd_numa
> -static inline int pmd_numa(pmd_t pmd)
> -{
> -	return pte_numa(pmd_pte(pmd));
> -}
> -
>  #define pmdp_set_numa pmdp_set_numa
>  static inline void pmdp_set_numa(struct mm_struct *mm, unsigned long addr,
>  				 pmd_t *pmdp)
> @@ -109,16 +71,21 @@ static inline void pmdp_set_numa(struct mm_struct *mm, unsigned long addr,
>  	return;
>  }
>  
> -#define pmd_mknonnuma pmd_mknonnuma
> -static inline pmd_t pmd_mknonnuma(pmd_t pmd)
> +/*
> + * Generic NUMA pte helpers expect pteval_t and pmdval_t types to exist
> + * which was inherited from x86. For the purposes of powerpc pte_basic_t and
> + * pmd_t are equivalent
> + */
> +#define pteval_t pte_basic_t
> +#define pmdval_t pmd_t
> +static inline pteval_t ptenuma_flags(pte_t pte)
>  {
> -	return pte_pmd(pte_mknonnuma(pmd_pte(pmd)));
> +	return pte_val(pte) & _PAGE_NUMA_MASK;
>  }
>  
> -#define pmd_mknuma pmd_mknuma
> -static inline pmd_t pmd_mknuma(pmd_t pmd)
> +static inline pmdval_t pmdnuma_flags(pmd_t pmd)
>  {
> -	return pte_pmd(pte_mknuma(pmd_pte(pmd)));
> +	return pmd_val(pmd) & _PAGE_NUMA_MASK;
>  }
>  
>  # else
> diff --git a/arch/powerpc/include/asm/pte-common.h b/arch/powerpc/include/asm/pte-common.h
> index 8d1569c..e040c35 100644
> --- a/arch/powerpc/include/asm/pte-common.h
> +++ b/arch/powerpc/include/asm/pte-common.h
> @@ -98,6 +98,11 @@ extern unsigned long bad_call_to_PMD_PAGE_SIZE(void);
>  			 _PAGE_USER | _PAGE_ACCESSED | \
>  			 _PAGE_RW | _PAGE_HWWRITE | _PAGE_DIRTY | _PAGE_EXEC)
>  
> +#ifdef CONFIG_NUMA_BALANCING
> +/* Mask of bits that distinguish present and numa ptes */
> +#define _PAGE_NUMA_MASK (_PAGE_NUMA|_PAGE_PRESENT)
> +#endif
> +
>  /*
>   * We define 2 sets of base prot bits, one for basic pages (ie,
>   * cacheable kernel and user pages) and one for non cacheable
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index d24887b..0a3f32b 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -28,7 +28,6 @@ config X86
>  	select HAVE_UNSTABLE_SCHED_CLOCK
>  	select ARCH_SUPPORTS_NUMA_BALANCING if X86_64
>  	select ARCH_SUPPORTS_INT128 if X86_64
> -	select ARCH_WANTS_PROT_NUMA_PROT_NONE
>  	select HAVE_IDE
>  	select HAVE_OPROFILE
>  	select HAVE_PCSPKR_PLATFORM
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index f216963..0f9724c 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -325,6 +325,20 @@ static inline pteval_t pte_flags(pte_t pte)
>  	return native_pte_val(pte) & PTE_FLAGS_MASK;
>  }
>  
> +#ifdef CONFIG_NUMA_BALANCING
> +/* Set of bits that distinguishes present, prot_none and numa ptes */
> +#define _PAGE_NUMA_MASK (_PAGE_NUMA|_PAGE_PROTNONE|_PAGE_PRESENT)
> +static inline pteval_t ptenuma_flags(pte_t pte)
> +{
> +	return pte_flags(pte) & _PAGE_NUMA_MASK;
> +}
> +
> +static inline pmdval_t pmdnuma_flags(pmd_t pmd)
> +{
> +	return pmd_flags(pmd) & _PAGE_NUMA_MASK;
> +}
> +#endif /* CONFIG_NUMA_BALANCING */
> +
>  #define pgprot_val(x)	((x).pgprot)
>  #define __pgprot(x)	((pgprot_t) { (x) } )
>  
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 53b2acc..281870f 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -660,11 +660,12 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
>  }
>  
>  #ifdef CONFIG_NUMA_BALANCING
> -#ifdef CONFIG_ARCH_USES_NUMA_PROT_NONE
>  /*
> - * _PAGE_NUMA works identical to _PAGE_PROTNONE (it's actually the
> - * same bit too). It's set only when _PAGE_PRESET is not set and it's
> - * never set if _PAGE_PRESENT is set.
> + * _PAGE_NUMA distinguishes between an unmapped page table entry, an entry that
> + * is protected for PROT_NONE and a NUMA hinting fault entry. If the
> + * architecture defines __PAGE_PROTNONE then it should take that into account
> + * but those that do not can rely on the fact that the NUMA hinting scanner
> + * skips inaccessible VMAs.
>   *
>   * pte/pmd_present() returns true if pte/pmd_numa returns true. Page
>   * fault triggers on those regions if pte/pmd_numa returns true
> @@ -673,16 +674,14 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
>  #ifndef pte_numa
>  static inline int pte_numa(pte_t pte)
>  {
> -	return (pte_flags(pte) &
> -		(_PAGE_NUMA|_PAGE_PROTNONE|_PAGE_PRESENT)) == _PAGE_NUMA;
> +	return ptenuma_flags(pte) == _PAGE_NUMA;
>  }
>  #endif
>  
>  #ifndef pmd_numa
>  static inline int pmd_numa(pmd_t pmd)
>  {
> -	return (pmd_flags(pmd) &
> -		(_PAGE_NUMA|_PAGE_PROTNONE|_PAGE_PRESENT)) == _PAGE_NUMA;
> +	return pmdnuma_flags(pmd) == _PAGE_NUMA;
>  }
>  #endif
>  
> @@ -722,6 +721,8 @@ static inline pte_t pte_mknuma(pte_t pte)
>  {
>  	pteval_t val = pte_val(pte);
>  
> +	VM_BUG_ON(!(val & _PAGE_PRESENT));
> +
>  	val &= ~_PAGE_PRESENT;
>  	val |= _PAGE_NUMA;
>  
> @@ -765,16 +766,6 @@ static inline void pmdp_set_numa(struct mm_struct *mm, unsigned long addr,
>  }
>  #endif
>  #else
> -extern int pte_numa(pte_t pte);
> -extern int pmd_numa(pmd_t pmd);
> -extern pte_t pte_mknonnuma(pte_t pte);
> -extern pmd_t pmd_mknonnuma(pmd_t pmd);
> -extern pte_t pte_mknuma(pte_t pte);
> -extern pmd_t pmd_mknuma(pmd_t pmd);
> -extern void ptep_set_numa(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
> -extern void pmdp_set_numa(struct mm_struct *mm, unsigned long addr, pmd_t *pmdp);
> -#endif /* CONFIG_ARCH_USES_NUMA_PROT_NONE */
> -#else
>  static inline int pmd_numa(pmd_t pmd)
>  {
>  	return 0;
> diff --git a/init/Kconfig b/init/Kconfig
> index 9d76b99..60fa415 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -844,17 +844,6 @@ config ARCH_SUPPORTS_INT128
>  config ARCH_WANT_NUMA_VARIABLE_LOCALITY
>  	bool
>  
> -#
> -# For architectures that are willing to define _PAGE_NUMA as _PAGE_PROTNONE
> -config ARCH_WANTS_PROT_NUMA_PROT_NONE
> -	bool
> -
> -config ARCH_USES_NUMA_PROT_NONE
> -	bool
> -	default y
> -	depends on ARCH_WANTS_PROT_NUMA_PROT_NONE
> -	depends on NUMA_BALANCING
> -
>  config NUMA_BALANCING_DEFAULT_ENABLED
>  	bool "Automatically enable NUMA aware memory/task placement"
>  	default y
>
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