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.
Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
---
v2->v3:
using '>' instead of "==" option since NR_PAGEBLOCK_BITS allows wasted bits
include/linux/pageblock-flags.h | 3 ++-
mm/page_alloc.c | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 9132c5c..06a6632 100644
--- a/include/linux/pageblock-flags.h
+++ b/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 */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2ec9cc4..29ee87e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -426,6 +426,7 @@ 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);
--
2.7.4
