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

[David Hildenbrand <david@redhat.com>]

On 27.08.25 08:43, Wei Yang wrote:
> 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))

Yes :)

>>
> 
> Oops, I thinks you are right.

It goes without saying: please test your patches before submitting ;)

-- 
Cheers

David / dhildenb