【Linux内存源码分析】构建内存管理框架(3)

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。

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:

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()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。

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