From: Pingfan Liu <kernelfans@xxxxxxxxx> Subject: 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@xxxxxxxxx Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/include/linux/pageblock-flags.h~mm-pageblock-throw-compiling-time-error-if-pageblock_bits-can-not-hold-migrate_types +++ a/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 */ --- a/mm/page_alloc.c~mm-pageblock-throw-compiling-time-error-if-pageblock_bits-can-not-hold-migrate_types +++ a/mm/page_alloc.c @@ -431,6 +431,7 @@ void set_pfnblock_flags_mask(struct page 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); _
