start_kernel->setup_arch->paging_init-->free_area_init_node 之 1

void __init free_area_init_node(int nid, struct pglist_data *pgdat,
unsigned long *zones_size, unsigned long node_start_pfn,
unsigned long *zholes_size)
{
pgdat->node_id = nid;
pgdat->node_start_pfn = node_start_pfn;
calculate_zone_totalpages(pgdat, zones_size, zholes_size);

alloc_node_mem_map(pgdat);

free_area_init_core(pgdat, zones_size, zholes_size);
}

static void __init calculate_zone_totalpages(struct pglist_data *pgdat,
unsigned long *zones_size, unsigned long *zholes_size)
{
unsigned long realtotalpages, totalpages = 0;
int i;

for (i = 0; i < MAX_NR_ZONES; i++)
totalpages += zones_size[i];
pgdat->node_spanned_pages = totalpages; //该节点区域的页数总和，包括孔洞页数

realtotalpages = totalpages;
if (zholes_size)
for (i = 0; i < MAX_NR_ZONES; i++)
realtotalpages -= zholes_size[i];
pgdat->node_present_pages = realtotalpages; //该节点实际存在的页数
printk(KERN_DEBUG "On node %d totalpages: %lu/n", pgdat->node_id, realtotalpages);
}

static void __init alloc_node_mem_map(struct pglist_data *pgdat)
{
/* Skip empty nodes */
if (!pgdat->node_spanned_pages)
return;

#ifdef CONFIG_FLAT_NODE_MEM_MAP
/* ia64 gets its own node_mem_map, before this, without bootmem */
if (!pgdat->node_mem_map) {
unsigned long size;
struct page *map;

size = (pgdat->node_spanned_pages + 1) * sizeof(struct page);

//存储内存中所有页对应的页描述结构的总空间大小
map = alloc_remap(pgdat->node_id, size);
if (!map)
map = alloc_bootmem_node(pgdat, size);
pgdat->node_mem_map = map;

//该节点内存所有页描述结构变量空间的起始地址
}
#ifdef CONFIG_FLATMEM
/*
* With no DISCONTIG, the global mem_map is just set as node 0's
*/
if (pgdat == NODE_DATA(0))
mem_map = NODE_DATA(0)->node_mem_map;
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}