start_kernel ——> setup_arch ——> arch_mem_init ——> |——> bootmem_init
|——> device_tree_init
|——> sparse_init
|——> plat_swiotlb_setup
|——> paging_init
我们看看paging_init做了什么？！
void __init paging_init(void)
{
unsigned long max_zone_pfns[max_nr_zones];
unsigned long lastpfn __maybe_unused;
int i = ; pagetable_init();#ifdef config_highmem
kmap_init();
#endif
kmap_coherent_init();#ifdef config_zone_dma
max_zone_pfns[zone_dma] = max_dma_pfn;
#endif
#ifdef config_zone_dma32
max_zone_pfns[zone_dma32] = max_dma32_pfn;
#endif
max_zone_pfns[zone_normal] = max_low_pfn;
lastpfn = max_low_pfn;
#ifdef config_highmem
max_zone_pfns[zone_highmem] = highend_pfn;
lastpfn = highend_pfn;
#endif
/* 上述关于页表初始化就不说了，实在是看不懂！！ */
/*
* 1， max_zone_pfns 是一个数组，MAX_NR_ZONES = 3
* max_zones_pfns[0] = 131072 : 0 -> ZONE_NORMAL
* max_zones_pfns[1] = 262144 : 1 -> ZONE_HIGHMEM
* max_zones_pfns[2] = 2155610112 : 2 -> ZONE_MOVABLE
* 很明显，该数组是UMA系统内存结点的各个内存域的最大PFN.但是ZONE_MOVABLE是一个垃圾值，因为ZONE_MOVEABLE是一个虚拟内存域，而且此时该虚拟内存域的PFN还未计算。
* 还要说明的一点是 max_zone_pfns[0],其实我们系统真正的低端内存的大小是 0 - 57344，此时的 131072 是512M的区域，也就是MIPS默认512M以下都是低端内存！
* 2. free_area_init_nodes
*/
free_area_init_nodes(max_zone_pfns);
}
初始化内存域和节点数据结构
回忆上篇文章，我们设置了一个数组：early_node_map，到此我们通过基于体系结构相关代码获取了如下信息：
① 系统中各个内存域的页帧边界，保存在 max_zone_pfn 数组中。
② 各结点页帧的分配情况，保存在全局变量early_node_map中。
1. 管理数据结构的创建
从内核2.6.10开始提供了一个通用的框架，用于将上述信息转换为伙伴系统预期的结点和内存域数据结构。在这以前，各个体系结构必须自行建立相关数据结构。现在体系结构只需建立简单结构，将繁重的工作交给free_area_init_nodes完成。
/* kernel/mm/page_alloc.c *//**
* free_area_init_nodes - Initialise all pg_data_t and zone data
* @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.
* 计算每个内存结点的内存域大小，其中的 holes 也会计算出来！
*/
void __init free_area_init_nodes(unsigned long *max_zone_pfn)
{
unsigned long nid;
int i; /* Sort early_node_map as initialisation assumes it is sorted */
sort_node_map(); // 对early_node_map进行排序，后续初始化代码是认为是已经排序过的
/*
* 内核在 lib/sort.c 中提供了一个通用的堆排序实现，该函数采用了这个实现
*/ /* Record where the zone boundaries are */
memset(arch_zone_lowest_possible_pfn, ,
sizeof(arch_zone_lowest_possible_pfn));
memset(arch_zone_highest_possible_pfn, ,
sizeof(arch_zone_highest_possible_pfn)); arch_zone_lowest_possible_pfn[] = find_min_pfn_with_active_regions();
arch_zone_highest_possible_pfn[] = max_zone_pfn[];
/*
arch_zone_lowest_possible_pfn[0] = 0;
arch_zone_highest_possible_pfn[0] = 131072;
*/ for (i = ; i < MAX_NR_ZONES; i++) {
if (i == ZONE_MOVABLE)
continue;
arch_zone_lowest_possible_pfn[i] =
arch_zone_highest_possible_pfn[i-];
arch_zone_highest_possible_pfn[i] =
max(max_zone_pfn[i], arch_zone_lowest_possible_pfn[i]);
}
/*
* arch_zone_lowest_possible_pfn[1] = 131072
* arch_zone_highest_possible_pfn[1] = 262144
*/
arch_zone_lowest_possible_pfn[ZONE_MOVABLE] = ;
arch_zone_highest_possible_pfn[ZONE_MOVABLE] = ; /* Find the PFNs that ZONE_MOVABLE begins at in each node */
memset(zone_movable_pfn, , sizeof(zone_movable_pfn));
find_zone_movable_pfns_for_nodes(zone_movable_pfn);
/*
* 由于ZONE_MOVABLE是一个虚拟内存域，不与真正的硬件内存域关联，该内存域的边界总是设置为0.内核只有在设置了内核命令参数kernelcore或movablecore之一时，该内存域才会存在。
* 该内存域一般开始于各个结点的某个特定内存域的某一页帧号！响应的编号在find_zone_movable_pfns_for_nodes中计算。
*/ /* Print out the zone ranges */
printk("Zone PFN ranges:\n");
for (i = ; i < MAX_NR_ZONES; i++) {
if (i == ZONE_MOVABLE)
continue;
printk(" %-8s ", zone_names[i]);
if (arch_zone_lowest_possible_pfn[i] ==
arch_zone_highest_possible_pfn[i])
printk("empty\n");
else
printk("%0#10lx -> %0#10lx\n",
arch_zone_lowest_possible_pfn[i],
arch_zone_highest_possible_pfn[i]);
} /* Print out the PFNs ZONE_MOVABLE begins at in each node */
printk("Movable zone start PFN for each node\n");
for (i = ; i < MAX_NUMNODES; i++) {
if (zone_movable_pfn[i])
printk(" Node %d: %lu\n", i, zone_movable_pfn[i]);
} /* Print out the early_node_map[] */
printk("early_node_map[%d] active PFN ranges\n", nr_nodemap_entries);
for (i = ; i < nr_nodemap_entries; i++)
printk(" %3d: %0#10lx -> %0#10lx\n", early_node_map[i].nid,
early_node_map[i].start_pfn,
early_node_map[i].end_pfn);
/*
* 打印结果：
* Zone PFN ranges:
* Normal 0x00000000 -> 0x00020000 【0 - 131071】
* HightMem 0x00020000 -> 0x00040000 【131072 - 262144】
* Movable zone start PFN for each node 【没有开启ZONE_MOVABLE】
* early_node_map[2] active PFN ranges
* 0: 0x00000000 -> 0x0000e000 【0 -> 53744】
* 1: 0x00030000 -> 0x00040000 【196608 -> 262144】
*/ /* Initialise every node */
mminit_verify_pageflags_layout();
setup_nr_node_ids();
/* 遍历各个内存结点，分别调用free_area_init_node创建相关数据结构 */
for_each_online_node(nid) { // 对于UMA系统，只调用1次
pg_data_t *pgdat = NODE_DATA(nid);
free_area_init_node(nid, NULL,
find_min_pfn_for_node(nid), NULL); /* Any memory on that node */
if (pgdat->node_present_pages)
node_set_state(nid, N_HIGH_MEMORY); // 判断该结点是否有内存，如果有，就将结点位图的标志设置为 N_HIGH_MEMORY
check_for_regular_memory(pgdat); // 进一步检查地域ZONE_HIGHMEM的内存域中是否有内存，并据此在结点位图中相应地设置为N_NORMAL_MEMORY标志
}
}
void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
unsigned long node_start_pfn, unsigned long *zholes_size)
{
pg_data_t *pgdat = NODE_DATA(nid); pgdat->node_id = nid; // pgdat->node_id = 0
pgdat->node_start_pfn = node_start_pfn; // pgdat->node_start_pfn = 0
calculate_node_totalpages(pgdat, zones_size, zholes_size); // 见下文 alloc_node_mem_map(pgdat); // 见下文
#ifdef CONFIG_FLAT_NODE_MEM_MAP
printk(KERN_DEBUG "free_area_init_node: node %d, pgdat %08lx, node_mem_map %08lx\n",
nid, (unsigned long)pgdat,
(unsigned long)pgdat->node_mem_map);
/*
* free_area_init_node: node 0, pgdat 807874e0, node_mem_map 81000000
*/
#endif
printk("%d : *zones_size = %lu, *zholes_size = %lu", *zones_size, *zholes_size);
free_area_init_core(pgdat, zones_size, zholes_size);
}
static void __meminit calculate_node_totalpages(struct pglist_data *pgdat,
unsigned long *zones_size, unsigned long *zholes_size)
{
unsigned long realtotalpages, totalpages = ;
enum zone_type i; for (i = ; i < MAX_NR_ZONES; i++)
totalpages += zone_spanned_pages_in_node(pgdat->node_id, i,
zones_size);
pgdat->node_spanned_pages = totalpages; realtotalpages = totalpages;
for (i = ; i < MAX_NR_ZONES; i++)
realtotalpages -=
zone_absent_pages_in_node(pgdat->node_id, i,
zholes_size);
pgdat->node_present_pages = realtotalpages;
printk(KERN_DEBUG "On node %d totalpages: %lu\n", pgdat->node_id,
realtotalpages); /*
* 计算内存结点的内存域信息：
* pgdat->node_spanned_pages = 262144 【包含 holes】
* pgdat->node_present_pages = 122880 【取出 holes】
*/
}
static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat)
{
/* Skip empty nodes */
if (!pgdat->node_spanned_pages) // 跳过不包含内存域的结点
return;#ifdef CONFIG_FLAT_NODE_MEM_MAP
/* ia64 gets its own node_mem_map, before this, without bootmem */
if (!pgdat->node_mem_map) { // 系统中的每个物理页帧对应着一个struct page结构体，node_mem_map存储的就是start_page开始的地址
unsigned long size, start, end;
struct page *map; /*
* The zone's endpoints aren't required to be MAX_ORDER
* aligned but the node_mem_map endpoints must be in order
* for the buddy allocator to function correctly.
*/
start = pgdat->node_start_pfn & ~(MAX_ORDER_NR_PAGES - );
end = pgdat->node_start_pfn + pgdat->node_spanned_pages;
end = ALIGN(end, MAX_ORDER_NR_PAGES);
size = (end - start) * sizeof(struct page);
/*
* start = 0， end = 2621144, size = 8388608 【说明在创建 struct page 实例时，包含了hole也一起创建了 struct page】
*/
map = alloc_remap(pgdat->node_id, size); // 如果特定于体系结构的代码尚未建立内存映射，返回NULL
if (!map)
map = alloc_bootmem_node_nopanic(pgdat, size); // 使用bootmem allocator分配器进行内存分配
pgdat->node_mem_map = map + (pgdat->node_start_pfn - start);
}
#ifndef CONFIG_NEED_MULTIPLE_NODES
/*
* With no DISCONTIG, the global mem_map is just set as node 0's
*/
if (pgdat == NODE_DATA()) {
mem_map = NODE_DATA()->node_mem_map;
#ifdef CONFIG_ARCH_POPULATES_NODE_MAP
if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
#endif /* CONFIG_ARCH_POPULATES_NODE_MAP */
}
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}
函数 free_area_init_core对 pgdata 中相关的数据结构进行初始化设置。
