mm/pageblock: throw compile error if pageblock_bits cannot hold MIGRA…

…TE_TYPES

Currently, NR_PAGEBLOCK_BITS and MIGRATE_TYPES are not associated by code.
If someone adds extra migrate type, then he may forget to enlarge the
NR_PAGEBLOCK_BITS.  Hence it requires some way to fix.

NR_PAGEBLOCK_BITS depends on MIGRATE_TYPES, while these macro spread on
two different .h file with reverse dependency, it is a little hard to
refer to MIGRATE_TYPES in pageblock-flag.h.  This patch tries to remind
such relation in compiling-time.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Pingfan Liu <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Alexander Duyck <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/pageblock-flags.h

@@ -25,10 +25,11 @@
 
 #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 + 3 - 1,
+	PB_migrate_end = PB_migrate + PB_migratetype_bits - 1,
 			/* 3 bits required for migrate types */
 	PB_migrate_skip,/* If set the block is skipped by compaction */
 

mm/page_alloc.c

@@ -431,6 +431,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 	unsigned long old_word, word;
 
 	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
+	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
 
 	bitmap = get_pageblock_bitmap(page, pfn);
 	bitidx = pfn_to_bitidx(page, pfn);