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

[Wei Yang <richard.weiyang@gmail.com>]

On Tue, Aug 26, 2025 at 10:21:20PM -0400, Zi Yan wrote:
>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))
>

Oops, I thinks you are right.

-- 
Wei Yang
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