On 12/7/18 5:53 AM, Pingfan Liu wrote:
> 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>
> ---
> include/linux/pageblock-flags.h | 5 +++--
> mm/page_alloc.c | 3 ++-
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
> index 9132c5c..fe0aec4 100644
> --- a/include/linux/pageblock-flags.h
> +++ b/include/linux/pageblock-flags.h
> @@ -25,11 +25,12 @@
>
> #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,
> - /* 3 bits required for migrate types */
> + PB_migrate_end = PB_migrate + PB_migratetype_bits - 1,
> + /* n 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..1a22d8d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -425,7 +425,8 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
> unsigned long bitidx, word_bitidx;
> unsigned long old_word, word;
>
> - BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
Why delete this one? It's for something a bit different and also still
valid.
> + BUILD_BUG_ON(order_base_2(MIGRATE_TYPES)
> + != (PB_migratetype_bits - 1));
I think this should use the '>' operator. It's fine if there are less
types than what can fit into 3 bits. AFAICS for !CONFIG_DMA and
!CONFIG_MEMORY_ISOLATION there are just 4 types that fit into 2 bits...
>
> bitmap = get_pageblock_bitmap(page, pfn);
> bitidx = pfn_to_bitidx(page, pfn);
>
