NR_PAGEBLOCK_BITS
((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * NR_PAGEBLOCK_BITS)
usemapsize *= NR_PAGEBLOCK_BITS;
return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 8);
BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);