Re: [PATCH] mm/pageblock: throw compiling time error if pageblock_bits can not hold MIGRATE_TYPES

[Pingfan Liu <kernelfans@gmail.com>]

On Wed, Dec 5, 2018 at 4:06 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> Currently, NR_PAGEBLOCK_BITS and MIGRATE_TYPES are not associated by code.
> If someone adds extra migrate type, then he may forget to enlarge the
> NR_PAGEBLOCK_BITS.
> NR_PAGEBLOCK_BITS depends on MIGRATE_TYPES, while these macro
> spread on two different .h file with reverse dependency, it is a little
> hard to refer to MIGRATE_TYPES in pageblock-flag.h. This patch tries to
> remind such relation in compiling-time.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> ---
>  include/linux/pageblock-flags.h | 5 +++--
>  mm/page_alloc.c                 | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
> index 9132c5c..fe0aec4 100644
> --- a/include/linux/pageblock-flags.h
> +++ b/include/linux/pageblock-flags.h
> @@ -25,11 +25,12 @@
>
>  #include <linux/types.h>
>
> +#define PB_migratetype_bits 3
>  /* Bit indices that affect a whole block of pages */
>  enum pageblock_bits {
>         PB_migrate,
> -       PB_migrate_end = PB_migrate + 3 - 1,
> -                       /* 3 bits required for migrate types */
> +       PB_migrate_end = PB_migrate + PB_migratetype_bits - 1,
> +                       /* n bits required for migrate types */
>         PB_migrate_skip,/* If set the block is skipped by compaction */
>
>         /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2ec9cc4..537020f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -425,7 +425,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
>         unsigned long bitidx, word_bitidx;
>         unsigned long old_word, word;
>
> -       BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
> +       BUILD_BUG_ON(order_base_2(MIGRATE_TYPES) != PB_migratetype_bits);
>
Sorry, I made a mistake. It should be (PB_migratetype_bits -1). I will
send out V2

Regards,
Pingfan
>         bitmap = get_pageblock_bitmap(page, pfn);
>         bitidx = pfn_to_bitidx(page, pfn);
> --
> 2.7.4
>