此处接前文，分析free_area_init_nodes()函数最后部分，分析其末尾的循环：
for_each_online_node(nid) {
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_MEMORY);
check_for_memory(pgdat, nid);
}
这里面的关键函数是free_area_init_node()，其入参find_min_pfn_for_node()用于获取node节点中最低的内存页框号。
而free_area_init_node()其实现：
【file：/mm/page_alloc.c】
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);
unsigned long start_pfn = 0;
unsigned long end_pfn = 0;
/* pg_data_t should be reset to zero when it's allocated */
WARN_ON(pgdat->nr_zones || pgdat->classzone_idx);
pgdat->node_id = nid;
pgdat->node_start_pfn = node_start_pfn;
init_zone_allows_reclaim(nid);
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
#endif
calculate_node_totalpages(pgdat, start_pfn, end_pfn,
zones_size, zholes_size);
alloc_node_mem_map(pgdat);
#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);
#endif
free_area_init_core(pgdat, start_pfn, end_pfn,
zones_size, zholes_size);
}
该函数中，其中init_zone_allows_reclaim()用于计算评估内存管理区是否可回收以及合适的node节点数，如果非NUMA环境，则该函数为空。而基于CONFIG_HAVE_MEMBLOCK_NODE_MAP的配置下，接下来将是get_pfn_range_for_nid()：
【file：/mm/page_alloc.c】
/**
* get_pfn_range_for_nid - Return the start and end page frames for a node
* @nid: The nid to return the range for. If MAX_NUMNODES, the min and max PFN are returned.
* @start_pfn: Passed by reference. On return, it will have the node start_pfn.
* @end_pfn: Passed by reference. On return, it will have the node end_pfn.
*
* It returns the start and end page frame of a node based on information
* provided by an arch calling add_active_range(). If called for a node
* with no available memory, a warning is printed and the start and end
* PFNs will be 0.
*/
void __meminit get_pfn_range_for_nid(unsigned int nid,
unsigned long *start_pfn, unsigned long *end_pfn)
{
unsigned long this_start_pfn, this_end_pfn;
int i;
*start_pfn = -1UL;
*end_pfn = 0;
for_each_mem_pfn_range(i, nid, &this_start_pfn, &this_end_pfn, NULL) {
*start_pfn = min(*start_pfn, this_start_pfn);
*end_pfn = max(*end_pfn, this_end_pfn);
}
if (*start_pfn == -1UL)
*start_pfn = 0;
}
此函数主要是将内存node节点的起始和末尾页框号返回给接下来的calculate_node_totalpages()来使用。
calculate_node_totalpages()实现：
【file：/mm/page_alloc.c】
static void __meminit calculate_node_totalpages(struct pglist_data *pgdat,
unsigned long node_start_pfn,
unsigned long node_end_pfn,
unsigned long *zones_size,
unsigned long *zholes_size)
{
unsigned long realtotalpages, totalpages = 0;
enum zone_type i;
for (i = 0; i < MAX_NR_ZONES; i++)
totalpages += zone_spanned_pages_in_node(pgdat->node_id, i,
node_start_pfn,
node_end_pfn,
zones_size);
pgdat->node_spanned_pages = totalpages;
realtotalpages = totalpages;
for (i = 0; i < MAX_NR_ZONES; i++)
realtotalpages -=
zone_absent_pages_in_node(pgdat->node_id, i,
node_start_pfn, node_end_pfn,
zholes_size);
pgdat->node_present_pages = realtotalpages;
printk(KERN_DEBUG "On node %d totalpages: %lu\n", pgdat->node_id,
realtotalpages);
}
其中zone_spanned_pages_in_node()：
【file：/mm/page_alloc.c】
/*
* Return the number of pages a zone spans in a node, including holes
* present_pages = zone_spanned_pages_in_node() - zone_absent_pages_in_node()
*/
static unsigned long __meminit zone_spanned_pages_in_node(int nid,
unsigned long zone_type,
unsigned long node_start_pfn,
unsigned long node_end_pfn,
unsigned long *ignored)
{
unsigned long zone_start_pfn, zone_end_pfn;
/* Get the start and end of the zone */
zone_start_pfn = arch_zone_lowest_possible_pfn[zone_type];
zone_end_pfn = arch_zone_highest_possible_pfn[zone_type];
adjust_zone_range_for_zone_movable(nid, zone_type,
node_start_pfn, node_end_pfn,
&zone_start_pfn, &zone_end_pfn);
/* Check that this node has pages within the zone's required range */
if (zone_end_pfn < node_start_pfn || zone_start_pfn > node_end_pfn)
return 0;
/* Move the zone boundaries inside the node if necessary */
zone_end_pfn = min(zone_end_pfn, node_end_pfn);
zone_start_pfn = max(zone_start_pfn, node_start_pfn);
/* Return the spanned pages */
return zone_end_pfn - zone_start_pfn;
}
其主要是统计node管理节点的内存跨度，该跨度不包括movable管理区的，里面调用的adjust_zone_range_for_zone_movable()则是用于剔除movable管理区的部分。
另外的zone_absent_pages_in_node()：
【file：/mm/page_alloc.c】
/* Return the number of page frames in holes in a zone on a node */
static unsigned long __meminit zone_absent_pages_in_node(int nid,
unsigned long zone_type,
unsigned long node_start_pfn,
unsigned long node_end_pfn,
unsigned long *ignored)
{
unsigned long zone_low = arch_zone_lowest_possible_pfn[zone_type];
unsigned long zone_high = arch_zone_highest_possible_pfn[zone_type];
unsigned long zone_start_pfn, zone_end_pfn;
zone_start_pfn = clamp(node_start_pfn, zone_low, zone_high);
zone_end_pfn = clamp(node_end_pfn, zone_low, zone_high);
adjust_zone_range_for_zone_movable(nid, zone_type,
node_start_pfn, node_end_pfn,
&zone_start_pfn, &zone_end_pfn);
return __absent_pages_in_range(nid, zone_start_pfn, zone_end_pfn);
}
该函数主要用于计算内存空洞页面数的。完了将会得到物理页面总数并在calculate_node_totalpages()中将页面总数打印出来：
紧接着在free_area_init_node()调用的是alloc_node_mem_map()：
【file：/mm/page_alloc.c】
static void __init_refok 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, 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 - 1);
end = pgdat_end_pfn(pgdat);
end = ALIGN(end, MAX_ORDER_NR_PAGES);
size = (end - start) * sizeof(struct page);
map = alloc_remap(pgdat->node_id, size);
if (!map)
map = memblock_virt_alloc_node_nopanic(size,
pgdat->node_id);
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(0)) {
mem_map = NODE_DATA(0)->node_mem_map;
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
}
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}
其主要将calculate_node_totalpages()统计所得的内存页面信息进行内存空间申请。
得到内存空间后，初始化工作将交由free_area_init_core()：
【file：/mm/page_alloc.c】
/*
* Set up the zone data structures:
* - mark all pages reserved
* - mark all memory queues empty
* - clear the memory bitmaps
*
* NOTE: pgdat should get zeroed by caller.
*/
static void __paginginit free_area_init_core(struct pglist_data *pgdat,
unsigned long node_start_pfn, unsigned long node_end_pfn,
unsigned long *zones_size, unsigned long *zholes_size)
{
enum zone_type j;
int nid = pgdat->node_id;
unsigned long zone_start_pfn = pgdat->node_start_pfn;
int ret;
pgdat_resize_init(pgdat);
#ifdef CONFIG_NUMA_BALANCING
spin_lock_init(&pgdat->numabalancing_migrate_lock);
pgdat->numabalancing_migrate_nr_pages = 0;
pgdat->numabalancing_migrate_next_window = jiffies;
#endif
init_waitqueue_head(&pgdat->kswapd_wait);
init_waitqueue_head(&pgdat->pfmemalloc_wait);
pgdat_page_cgroup_init(pgdat);
for (j = 0; j < MAX_NR_ZONES; j++) {
struct zone *zone = pgdat->node_zones + j;
unsigned long size, realsize, freesize, memmap_pages;
size = zone_spanned_pages_in_node(nid, j, node_start_pfn,
node_end_pfn, zones_size);
realsize = freesize = size - zone_absent_pages_in_node(nid, j,
node_start_pfn,
node_end_pfn,
zholes_size);
/*
* Adjust freesize so that it accounts for how much memory
* is used by this zone for memmap. This affects the watermark
* and per-cpu initialisations
*/
memmap_pages = calc_memmap_size(size, realsize);
if (freesize >= memmap_pages) {
freesize -= memmap_pages;
if (memmap_pages)
printk(KERN_DEBUG
" %s zone: %lu pages used for memmap\n",
zone_names[j], memmap_pages);
} else
printk(KERN_WARNING
" %s zone: %lu pages exceeds freesize %lu\n",
zone_names[j], memmap_pages, freesize);
/* Account for reserved pages */
if (j == 0 && freesize > dma_reserve) {
freesize -= dma_reserve;
printk(KERN_DEBUG " %s zone: %lu pages reserved\n",
zone_names[0], dma_reserve);
}
if (!is_highmem_idx(j))
nr_kernel_pages += freesize;
/* Charge for highmem memmap if there are enough kernel pages */
else if (nr_kernel_pages > memmap_pages * 2)
nr_kernel_pages -= memmap_pages;
nr_all_pages += freesize;
zone->spanned_pages = size;
zone->present_pages = realsize;
/*
* Set an approximate value for lowmem here, it will be adjusted
* when the bootmem allocator frees pages into the buddy system.
* And all highmem pages will be managed by the buddy system.
*/
zone->managed_pages = is_highmem_idx(j) ? realsize : freesize;
#ifdef CONFIG_NUMA
zone->node = nid;
zone->min_unmapped_pages = (freesize*sysctl_min_unmapped_ratio)
/ 100;
zone->min_slab_pages = (freesize * sysctl_min_slab_ratio) / 100;
#endif
zone->name = zone_names[j];
spin_lock_init(&zone->lock);
spin_lock_init(&zone->lru_lock);
zone_seqlock_init(zone);
zone->zone_pgdat = pgdat;
zone_pcp_init(zone);
/* For bootup, initialized properly in watermark setup */
mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages);
lruvec_init(&zone->lruvec);
if (!size)
continue;
set_pageblock_order();
setup_usemap(pgdat, zone, zone_start_pfn, size);
ret = init_currently_empty_zone(zone, zone_start_pfn,
size, MEMMAP_EARLY);
BUG_ON(ret);
memmap_init(size, nid, j, zone_start_pfn);
zone_start_pfn += size;
}
}
该函数主要用于设置了内存管理节点的管理结构体，包括pgdat_resize_init()初始化锁资源、init_waitqueue_head()初始内存队列、pgdat_page_cgroup_init()控制组群初始化。
而在for循环内，循环遍历统计各个管理区最大跨度间相差的页面数size以及除去内存“空洞”后的实际页面数realsize,然后通过calc_memmap_size()计算出该管理区所需的页面管理结构占用的页面数memmap_pages，最后可以计算得除高端内存外的系统内存共有的内存页面数nr_kernel_pages（用于统计所有一致映射的页）；此外循环体内的操作则是初始化内存管理区的管理结构，例如各类锁的初始化、队列初始化。值得注意的是zone_pcp_init()是初始化冷热页分配器的，mod_zone_page_state()用于计算更新管理区的状态统计，lruvec_init()则是初始化LRU算法使用的链表和保护锁，而set_pageblock_order()用于在CONFIG_HUGETLB_PAGE_SIZE_VARIABLE配置下设置pageblock_order值的；此外setup_usemap()函数则是主要是为了给zone管理结构体中的pageblock_flags申请内存空间，pageblock_flags与伙伴系统的碎片迁移算法有关。而init_currently_empty_zone()则主要初始化管理区的等待队列哈希表和等待队列，同时还初始化了与伙伴系统相关的free_aera列表。
中间有部分日志记录可以通过dmesg查看到：
在free_area_init_core()的最后，着重分析一下memmap_init()：
【file：/mm/page_alloc.c】
#define memmap_init(size, nid, zone, start_pfn) \
memmap_init_zone((size), (nid), (zone), (start_pfn), MEMMAP_EARLY)
其对应的是memmap_init_zone()：
【file：/mm/page_alloc.c】
/*
* Initially all pages are reserved - free ones are freed
* up by free_all_bootmem() once the early boot process is
* done. Non-atomic initialization, single-pass.
*/
void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
unsigned long start_pfn, enum memmap_context context)
{
struct page *page;
unsigned long end_pfn = start_pfn + size;
unsigned long pfn;
struct zone *z;
if (highest_memmap_pfn < end_pfn - 1)
highest_memmap_pfn = end_pfn - 1;
z = &NODE_DATA(nid)->node_zones[zone];
for (pfn = start_pfn; pfn < end_pfn; pfn++) {
/*
* There can be holes in boot-time mem_map[]s
* handed to this function. They do not
* exist on hotplugged memory.
*/
if (context == MEMMAP_EARLY) {
if (!early_pfn_valid(pfn))
continue;
if (!early_pfn_in_nid(pfn, nid))
continue;
}
page = pfn_to_page(pfn);
set_page_links(page, zone, nid, pfn);
mminit_verify_page_links(page, zone, nid, pfn);
init_page_count(page);
page_mapcount_reset(page);
page_cpupid_reset_last(page);
SetPageReserved(page);
/*
* Mark the block movable so that blocks are reserved for
* movable at startup. This will force kernel allocations
* to reserve their blocks rather than leaking throughout
* the address space during boot when many long-lived
* kernel allocations are made. Later some blocks near
* the start are marked MIGRATE_RESERVE by
* setup_zone_migrate_reserve()
*
* bitmap is created for zone's valid pfn range. but memmap
* can be created for invalid pages (for alignment)
* check here not to call set_pageblock_migratetype() against
* pfn out of zone.
*/
if ((z->zone_start_pfn <= pfn)
&& (pfn < zone_end_pfn(z))
&& !(pfn & (pageblock_nr_pages - 1)))
set_pageblock_migratetype(page, MIGRATE_MOVABLE);
INIT_LIST_HEAD(&page->lru);
#ifdef WANT_PAGE_VIRTUAL
/* The shift won't overflow because ZONE_NORMAL is below 4G. */
if (!is_highmem_idx(zone))
set_page_address(page, __va(pfn << PAGE_SHIFT));
#endif
}
}
该函数主要根据页框号pfn通过pfn_to_page()查找到页面管理结构page，而后面的操作则是对该页面的管理结构page进行初始化。
至此，free_area_init_node()的初始化操作执行完毕，据前面分析可以知道其主要是将整个linux物理内存管理框架进行初始化，包括管理节点node、管理区zone以及页面管理page等数据的初始化。
回到本文主题，循环体内最后的两个函数node_set_state()和check_for_memory()。node_set_state()主要是对node节点进行状态设置，而check_for_memory()则是做内存检查。
至此，内存管理框架构建完毕。