mm/pageblock-flags: remove PB_migratetype_bits/PB_migrate_end

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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Wei Yang <[e-mail]>
Suggested-by: David Hildenbrand <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Reviewed-by: Zi Yan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/pageblock-flags.h

···
 
 #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
···
 
 #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_0)|BIT(PB_migrate_1)|BIT(PB_migrate_2))
 
 #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

mm/page_alloc.c

···
 
 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
···
 #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);