PB_compact_skip
set_pfnblock_bit(page, page_to_pfn(page), PB_compact_skip)
get_pfnblock_bit(page, page_to_pfn(page), PB_compact_skip)
clear_pfnblock_bit(page, page_to_pfn(page), PB_compact_skip)
return pb_bit >= PB_compact_skip && pb_bit < __NR_PAGEBLOCK_BITS;