Re: [PATCH 2/2] mm/pageblock-flags: simplify MIGRATETYPE_MASK definition

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

On Tue, Aug 26, 2025 at 03:34:13PM +0200, David Hildenbrand wrote:
>On 26.08.25 11:31, Wei Yang wrote:
>> MIGRATETYPE_MASK is defined to be the mask of possible migratetype.
>> 
>> Define it with PB_migratetype_bits directly would be more clear.
>> 
>> 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>
>> ---
>>   include/linux/pageblock-flags.h | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
>> 
>> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
>> index 6a44be0f39f4..1489c062a5a7 100644
>> --- a/include/linux/pageblock-flags.h
>> +++ b/include/linux/pageblock-flags.h
>> @@ -37,11 +37,10 @@ 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 (BIT(PB_migratetype_bits) - 1)
>>   #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
>
>
>Hm, I wonder if we can get rid of PB_migratetype_bits
>
>diff --git a/include/linux/pageblock-flags.h
>b/include/linux/pageblock-flags.h
>index 6a44be0f39f45..70c988dbdddc8 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
>
>And then just work with the bits. No magical computations.

Something like this?

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 6a44be0f39f4..a09b79a1fb7d 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 (BIT(PB_migrate_2 + 1) - 1)
 
 #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..7a67250ccfd5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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 >= BIT(PB_migrate_2 + 1));
 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
 
 	bitmap = get_pageblock_bitmap(page, pfn);

-- 
Wei Yang
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