On Fri, Dec 7, 2018 at 3:36 PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> 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.
>
I think it is dependent on PB_migratetype_bits (plus 1 dedicated bit
for skip), hence the later one implies it.
> > + 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
If ">" is chosen, then it allows wasted bits. I had thought it is not
the purpose of the design, hence disard the ">". Otherwise, what about
using warning on ">"?
> 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...
>
Oh, yes, you are right. How about this:
#if defined(CONFIG_DMA) || defined(CONFIG_MEMORY_ISOLATION)
#define PB_migratetype_bits 3
#else
#define PB_migratetype_bits 2
#endif
Thanks for your kindly review.
Regards,
Pingfan
> >
> > bitmap = get_pageblock_bitmap(page, pfn);
> > bitidx = pfn_to_bitidx(page, pfn);
> >
>
