mm/pageblock: throw compile error if pageblock_bits cannot hold MIGRATE_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/1544508709-11358-1-git-send-email-kernelfans@gmail.com
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index 9132c5c..06a6632 100644 (file)
--- 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 b4fcf21..cd1c9d3 100644 (file)
--- a/mm/page_alloc.c
+++ b/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);