zone_spans_pfn
if (zone_spans_pfn(zone, pfn))
if (!zone_spans_pfn(zone, start))
if (!zone_spans_pfn(zone, end - 1))
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
ret = !zone_spans_pfn(zone, pfn);
return zone_spans_pfn(zone, last_pfn);