Re: [Patch v2 2/2] mm/pageblock-flags: remove PB_migratetype_bits/PB_migrate_end

[Zi Yan <ziy@nvidia.com>]

On 26 Aug 2025, at 22:11, Wei Yang wrote:

> enum pageblock_bits defines the meaning of pageblock bits. Currently
> PB_migratetype_bits says the lowest 3 bits represents migratetype and
> PB_migrate_end/MIGRATETYPE_MASK's definition rely on it with magical
> computation.
>
> Remove the definition of PB_migratetype_bits/PB_migrate_end. Use
> PB_migrate_[0|1|2] to represent lowest bits for migratetype. Then we can
> simplify related definition.
>
> Also, MIGRATETYPE_AND_ISO_MASK is MIGRATETYPE_MASK add isolation bit.
> Use MIGRATETYPE_MASK in the definition of MIGRATETYPE_AND_ISO_MASK looks
> cleaner.
>
> No functional change intended.
>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: David Hildenbrand <david@redhat.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
>
> ---
> v2: remove PB_migratetype_bits and PB_migrate_end
> ---
>  include/linux/pageblock-flags.h | 12 +++++-------
>  mm/page_alloc.c                 |  4 ++--
>  2 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
> index 6a44be0f39f4..6e4c2da15706 100644
> --- a/include/linux/pageblock-flags.h
> +++ b/include/linux/pageblock-flags.h
> @@ -13,12 +13,11 @@
>
>  #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 + PB_migratetype_bits - 1,
> -			/* 3 bits required for migrate types */
> +	PB_migrate_0,
> +	PB_migrate_1,
> +	PB_migrate_2,
>  	PB_compact_skip,/* If set the block is skipped by compaction */
>
>  #ifdef CONFIG_MEMORY_ISOLATION
> @@ -37,11 +36,10 @@ enum pageblock_bits {
>
>  #define NR_PAGEBLOCK_BITS (roundup_pow_of_two(__NR_PAGEBLOCK_BITS))
>
> -#define MIGRATETYPE_MASK ((1UL << (PB_migrate_end + 1)) - 1)
> +#define MIGRATETYPE_MASK (PB_migrate_0|PB_migrate_1|PB_migrate_2)

I think David meant

#define MIGRATETYPE_MASK (BIT(PB_migrate_0)|BIT(PB_migrate_1)|BIT(PB_migrate_2))

Otherwise, LGTM. Feel free to add Reviewed-by: Zi Yan <ziy@nvidia.com>,
once you fix the above.

>
>  #ifdef CONFIG_MEMORY_ISOLATION
> -#define MIGRATETYPE_AND_ISO_MASK \
> -	(((1UL << (PB_migrate_end + 1)) - 1) | BIT(PB_migrate_isolate))
> +#define MIGRATETYPE_AND_ISO_MASK (MIGRATETYPE_MASK | BIT(PB_migrate_isolate))
>  #else
>  #define MIGRATETYPE_AND_ISO_MASK MIGRATETYPE_MASK
>  #endif
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e534f31a6b39..c1a18aaf8b41 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -355,7 +355,7 @@ static inline int pfn_to_bitidx(const struct page *page, unsigned long pfn)
>
>  static __always_inline bool is_standalone_pb_bit(enum pageblock_bits pb_bit)
>  {
> -	return pb_bit > PB_migrate_end && pb_bit < __NR_PAGEBLOCK_BITS;
> +	return pb_bit >= PB_compact_skip && pb_bit < __NR_PAGEBLOCK_BITS;
>  }
>
>  static __always_inline void
> @@ -370,7 +370,7 @@ get_pfnblock_bitmap_bitidx(const struct page *page, unsigned long pfn,
>  #else
>  	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
>  #endif
> -	BUILD_BUG_ON(__MIGRATE_TYPE_END >= (1 << PB_migratetype_bits));
> +	BUILD_BUG_ON(__MIGRATE_TYPE_END > MIGRATETYPE_MASK);
>  	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
>
>  	bitmap = get_pageblock_bitmap(page, pfn);
> -- 
> 2.34.1


--
Best Regards,
Yan, Zi