Re: [PATCH] mm: rename CONFIG_PAGE_BLOCK_ORDER to CONFIG_PAGE_BLOCK_ORDER_CEIL.

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 6/3/25 21:18, Zi Yan wrote:
> The config is in fact an additional upper limit of pageblock_order, so
> rename it to avoid confusion.

Agreed. This new config has been similar to existing 'pageblock_order'
that might cause confusion. Hence renaming makes sense. But instead of
PAGE_BLOCK_ORDER_CEIL should it be rather PAGE_BLOCK_ORDER_MAX ?

> 
> Fixes: e13e7922d034 ("mm: add CONFIG_PAGE_BLOCK_ORDER to select page block order")

Does it really need a "Fixes: " tag given there is no problem to fix ?

> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>  include/linux/mmzone.h          | 14 +++++++-------
>  include/linux/pageblock-flags.h |  8 ++++----
>  mm/Kconfig                      | 15 ++++++++-------
>  3 files changed, 19 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 283913d42d7b..523b407e63e8 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -38,19 +38,19 @@
>  #define NR_PAGE_ORDERS (MAX_PAGE_ORDER + 1)
>  
>  /* Defines the order for the number of pages that have a migrate type. */
> -#ifndef CONFIG_PAGE_BLOCK_ORDER
> -#define PAGE_BLOCK_ORDER MAX_PAGE_ORDER
> +#ifndef CONFIG_PAGE_BLOCK_ORDER_CEIL
> +#define PAGE_BLOCK_ORDER_CEIL MAX_PAGE_ORDER
>  #else
> -#define PAGE_BLOCK_ORDER CONFIG_PAGE_BLOCK_ORDER
> -#endif /* CONFIG_PAGE_BLOCK_ORDER */
> +#define PAGE_BLOCK_ORDER_CEIL CONFIG_PAGE_BLOCK_ORDER_CEIL
> +#endif /* CONFIG_PAGE_BLOCK_ORDER_CEIL */
>  
>  /*
>   * The MAX_PAGE_ORDER, which defines the max order of pages to be allocated
> - * by the buddy allocator, has to be larger or equal to the PAGE_BLOCK_ORDER,
> + * by the buddy allocator, has to be larger or equal to the PAGE_BLOCK_ORDER_CEIL,
>   * which defines the order for the number of pages that can have a migrate type
>   */
> -#if (PAGE_BLOCK_ORDER > MAX_PAGE_ORDER)
> -#error MAX_PAGE_ORDER must be >= PAGE_BLOCK_ORDER
> +#if (PAGE_BLOCK_ORDER_CEIL > MAX_PAGE_ORDER)
> +#error MAX_PAGE_ORDER must be >= PAGE_BLOCK_ORDER_CEIL
>  #endif
>  
>  /*
> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
> index e73a4292ef02..e7a86cd238c2 100644
> --- a/include/linux/pageblock-flags.h
> +++ b/include/linux/pageblock-flags.h
> @@ -41,18 +41,18 @@ extern unsigned int pageblock_order;
>   * Huge pages are a constant size, but don't exceed the maximum allocation
>   * granularity.
>   */
> -#define pageblock_order		MIN_T(unsigned int, HUGETLB_PAGE_ORDER, PAGE_BLOCK_ORDER)
> +#define pageblock_order		MIN_T(unsigned int, HUGETLB_PAGE_ORDER, PAGE_BLOCK_ORDER_CEIL)
>  
>  #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
>  
>  #elif defined(CONFIG_TRANSPARENT_HUGEPAGE)
>  
> -#define pageblock_order		MIN_T(unsigned int, HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER)
> +#define pageblock_order		MIN_T(unsigned int, HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER_CEIL)
>  
>  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>  
> -/* If huge pages are not used, group by PAGE_BLOCK_ORDER */
> -#define pageblock_order		PAGE_BLOCK_ORDER
> +/* If huge pages are not used, group by PAGE_BLOCK_ORDER_CEIL */
> +#define pageblock_order		PAGE_BLOCK_ORDER_CEIL
>  
>  #endif /* CONFIG_HUGETLB_PAGE */
>  
> diff --git a/mm/Kconfig b/mm/Kconfig
> index eccb2e46ffcb..3b27e644bd1f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1017,8 +1017,8 @@ config ARCH_FORCE_MAX_ORDER
>  # the default page block order is MAX_PAGE_ORDER (10) as per
>  # include/linux/mmzone.h.
>  #
> -config PAGE_BLOCK_ORDER
> -	int "Page Block Order"
> +config PAGE_BLOCK_ORDER_CEIL
> +	int "Page Block Order Upper Limit"
>  	range 1 10 if ARCH_FORCE_MAX_ORDER = 0
>  	default 10 if ARCH_FORCE_MAX_ORDER = 0
>  	range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0
> @@ -1026,12 +1026,13 @@ config PAGE_BLOCK_ORDER
>  	help
>  	  The page block order refers to the power of two number of pages that
>  	  are physically contiguous and can have a migrate type associated to
> -	  them. The maximum size of the page block order is limited by
> -	  ARCH_FORCE_MAX_ORDER.
> +	  them. The maximum size of the page block order is at least limited by
> +	  ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER.
>  
> -	  This config allows overriding the default page block order when the
> -	  page block order is required to be smaller than ARCH_FORCE_MAX_ORDER
> -	  or MAX_PAGE_ORDER.
> +	  This config adds a new upper limit of default page block
> +	  order when the page block order is required to be smaller than
> +	  ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER or other limits
> +	  (see include/linux/pageblock-flags.h for details).
>  
>  	  Reducing pageblock order can negatively impact THP generation
>  	  success rate. If your workloads uses THP heavily, please use this