vmem_altmap_offset
page += vmem_altmap_offset(altmap);
|| vmem_altmap_offset(altmap) > nr_pages) {
return pfn + vmem_altmap_offset(pgmap_altmap(pgmap));
start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
end_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);