Re: [PATCH v5 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()

[Daniel Vacek <neelx@redhat.com>]

On Mon, Apr 2, 2018 at 4:30 AM, Jia He <hejianet@gmail.com> wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") optimized the loop in memmap_init_zone(). But there is
> still some room for improvement. E.g. if pfn and pfn+1 are in the same
> memblock region, we can simply pfn++ instead of doing the binary search
> in memblock_next_valid_pfn.
>
> Signed-off-by: Jia He <jia.he@hxt-semitech.com>
> ---
>  arch/arm/include/asm/page.h   |  1 +
>  arch/arm/mm/init.c            | 28 ++++++++++++++++++++++------
>  arch/arm64/include/asm/page.h |  1 +
>  arch/arm64/mm/init.c          | 28 ++++++++++++++++++++++------
>  4 files changed, 46 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
> index 489875c..f38909c 100644
> --- a/arch/arm/include/asm/page.h
> +++ b/arch/arm/include/asm/page.h
> @@ -157,6 +157,7 @@ extern void copy_page(void *to, const void *from);
>  typedef struct page *pgtable_t;
>
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
> +extern int early_region_idx;

I believe this is not needed anymore.

>  extern int pfn_valid(unsigned long);
>  extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
>  #define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 0fb85ca..06ed190 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -193,6 +193,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
>  }
>
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
> +int early_region_idx __meminitdata = -1;

static?

> +
>  int pfn_valid(unsigned long pfn)
>  {
>         return memblock_is_map_memory(__pfn_to_phys(pfn));
> @@ -203,28 +205,42 @@ EXPORT_SYMBOL(pfn_valid);
>  unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>  {
>         struct memblock_type *type = &memblock.memory;
> +       struct memblock_region *regions = type->regions;
>         unsigned int right = type->cnt;
>         unsigned int mid, left = 0;
> +       unsigned long start_pfn, end_pfn;
>         phys_addr_t addr = PFN_PHYS(++pfn);
>
> +       /* fast path, return pfn+1 if next pfn is in the same region */
> +       if (early_region_idx != -1) {
> +               start_pfn = PFN_DOWN(regions[early_region_idx].base);
> +               end_pfn = PFN_DOWN(regions[early_region_idx].base +
> +                               regions[early_region_idx].size);
> +
> +               if (pfn >= start_pfn && pfn < end_pfn)
> +                       return pfn;
> +       }
> +
> +       /* slow path, do the binary searching */
>         do {
>                 mid = (right + left) / 2;
>
> -               if (addr < type->regions[mid].base)
> +               if (addr < regions[mid].base)
>                         right = mid;
> -               else if (addr >= (type->regions[mid].base +
> -                                 type->regions[mid].size))
> +               else if (addr >= (regions[mid].base + regions[mid].size))
>                         left = mid + 1;
>                 else {
> -                       /* addr is within the region, so pfn is valid */
> +                       early_region_idx = mid;
>                         return pfn;
>                 }
>         } while (left < right);
>
>         if (right == type->cnt)
>                 return -1UL;
> -       else
> -               return PHYS_PFN(type->regions[right].base);
> +
> +       early_region_idx = right;
> +
> +       return PHYS_PFN(regions[early_region_idx].base);
>  }
>  EXPORT_SYMBOL(memblock_next_valid_pfn);
>  #endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> index e57d3f2..f0d8c8e5 100644
> --- a/arch/arm64/include/asm/page.h
> +++ b/arch/arm64/include/asm/page.h
> @@ -38,6 +38,7 @@ extern void clear_page(void *to);
>  typedef struct page *pgtable_t;
>
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
> +extern int early_region_idx;

ditto

>  extern int pfn_valid(unsigned long);
>  extern unsigned long memblock_next_valid_pfn(unsigned long pfn);
>  #define skip_to_last_invalid_pfn(pfn) (memblock_next_valid_pfn(pfn) - 1)
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 13e43ff..342e4e2 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -285,6 +285,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>  #endif /* CONFIG_NUMA */
>
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
> +int early_region_idx __meminitdata = -1;

ditto

--nX

> +
>  int pfn_valid(unsigned long pfn)
>  {
>         return memblock_is_map_memory(pfn << PAGE_SHIFT);
> @@ -295,28 +297,42 @@ EXPORT_SYMBOL(pfn_valid);
>  unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
>  {
>         struct memblock_type *type = &memblock.memory;
> +       struct memblock_region *regions = type->regions;
>         unsigned int right = type->cnt;
>         unsigned int mid, left = 0;
> +       unsigned long start_pfn, end_pfn;
>         phys_addr_t addr = PFN_PHYS(++pfn);
>
> +       /* fast path, return pfn+1 if next pfn is in the same region */
> +       if (early_region_idx != -1) {
> +               start_pfn = PFN_DOWN(regions[early_region_idx].base);
> +               end_pfn = PFN_DOWN(regions[early_region_idx].base +
> +                               regions[early_region_idx].size);
> +
> +               if (pfn >= start_pfn && pfn < end_pfn)
> +                       return pfn;
> +       }
> +
> +       /* slow path, do the binary searching */
>         do {
>                 mid = (right + left) / 2;
>
> -               if (addr < type->regions[mid].base)
> +               if (addr < regions[mid].base)
>                         right = mid;
> -               else if (addr >= (type->regions[mid].base +
> -                                 type->regions[mid].size))
> +               else if (addr >= (regions[mid].base + regions[mid].size))
>                         left = mid + 1;
>                 else {
> -                       /* addr is within the region, so pfn is valid */
> +                       early_region_idx = mid;
>                         return pfn;
>                 }
>         } while (left < right);
>
>         if (right == type->cnt)
>                 return -1UL;
> -       else
> -               return PHYS_PFN(type->regions[right].base);
> +
> +       early_region_idx = right;
> +
> +       return PHYS_PFN(regions[early_region_idx].base);
>  }
>  EXPORT_SYMBOL(memblock_next_valid_pfn);
>  #endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
> --
> 2.7.4
>