Man page 9 : free_area_init_nodes

free_area_init_nodes - Initialise all pg_data_t and zone data

void free_area_init_nodes(unsigned long *  max_zone_pfn );

max_zone_pfn
    an array of max PFNs for each zone

This will call free_area_init_node for each active node in the system. Using the page ranges provided by add_active_range, the size of each zone in each node and their holes is calculated. If the maximum PFN between two adjacent zones match, it is assumed that the zone is empty. For example, if arch_max_dma_pfn == arch_max_dma32_pfn, it is assumed that arch_max_dma32_pfn has no pages. It is also assumed that a zone starts where the previous one ended. For example, ZONE_DMA32 starts at arch_max_dma_pfn.