[linux内存管理] 第014篇 /proc/zoneinfo的详细解析

0. 前言

内存管理是一个相对复杂的内核模块，错综复杂的 数据结构 和管理逻辑。 Linux 内核为了帮助开发者从宏观上把握内存的使用情况，在几大核心数据结构中都有相应的计数统计，如物理页面使用情况、伙伴系统分配情况、内存管理区的页面使用情况、内存回收扫描回收情况、内存规整触发情况等等。

在 start_kernel() 中，会通过 setup_arch() 、 build_all_zonelists() 、 page_alloc_init() 、 mm_init() 等函数对内存相关模块进行初始化，最后会通过 arch_call_rest_init() 对 Linux 系统做剩余的初始化工作，此函数中会调用 rest_init()，并在此调用 kernel_init() 启动init 线程，这里创建了本文将要剖析的虚拟文件节点 /proc/zoneinfo 。

1. zoneinfo_show

static int zoneinfo_show(struct seq_file *m, void *arg)
{
	pg_data_t *pgdat = (pg_data_t *)arg;
	walk_zones_in_node(m, pgdat, false, false, zoneinfo_show_print);
	return 0;
}

static void walk_zones_in_node(struct seq_file *m, pg_data_t *pgdat,
		bool assert_populated, bool nolock,
		void (*print)(struct seq_file *m, pg_data_t *, struct zone *))
{
	struct zone *zone;
	struct zone *node_zones = pgdat->node_zones;
	unsigned long flags;

    // 遍历每一个node节点
	for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
		if (assert_populated && !populated_zone(zone))
			continue;

		if (!nolock)
			spin_lock_irqsave(&zone->lock, flags);
        //输出每个节点的zone信息
		print(m, pgdat, zone);
		if (!nolock)
			spin_unlock_irqrestore(&zone->lock, flags);
	}
}

调用 zoneinfo_show() 时，会通过函数 walk_zones_in_node() 对每个zone 进行遍历，从第 0 个zone 开始，当参数 zone 为第 0 个 zone 且该zone 的 present_pages 不为0 时， is_zone_first_populated () 返回为 true，则会将该 node 的page 信息打印出来。

2. zoneinfo_show_print

static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
							struct zone *zone)
{
	int i;
	seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
	if (is_zone_first_populated(pgdat, zone)) {
		seq_printf(m, "\n  per-node stats");
		for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
			unsigned long pages = node_page_state_pages(pgdat, i);

			if (vmstat_item_print_in_thp(i))
				pages /= HPAGE_PMD_NR;
			seq_printf(m, "\n      %-12s %lu", node_stat_name(i),
				   pages);
		}
	}
	seq_printf(m,
		   "\n  pages free     %lu"
		   "\n        min      %lu"
		   "\n        low      %lu"
		   "\n        high     %lu"
		   "\n        spanned  %lu"
		   "\n        present  %lu"
		   "\n        managed  %lu"
		   "\n        cma      %lu",
		   zone_page_state(zone, NR_FREE_PAGES),
		   min_wmark_pages(zone),
		   low_wmark_pages(zone),
		   high_wmark_pages(zone),
		   zone->spanned_pages,
		   zone->present_pages,
		   zone_managed_pages(zone),
		   zone_cma_pages(zone));

	seq_printf(m,
		   "\n        protection: (%ld",
		   zone->lowmem_reserve[0]);
	for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
		seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
	seq_putc(m, ')');

	/* If unpopulated, no other information is useful */
	if (!populated_zone(zone)) {
		seq_putc(m, '\n');
		return;
	}

	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
		seq_printf(m, "\n      %-12s %lu", zone_stat_name(i),
			   zone_page_state(zone, i));

#ifdef CONFIG_NUMA
	for (i = 0; i < NR_VM_NUMA_EVENT_ITEMS; i++)
		seq_printf(m, "\n      %-12s %lu", numa_stat_name(i),
			   zone_numa_event_state(zone, i));
#endif

	seq_printf(m, "\n  pagesets");
	for_each_online_cpu(i) {
		struct per_cpu_pages *pcp;
		struct per_cpu_zonestat __maybe_unused *pzstats;

		pcp = per_cpu_ptr(zone->per_cpu_pageset, i);
		seq_printf(m,
			   "\n    cpu: %i"
			   "\n              count: %i"
			   "\n              high:  %i"
			   "\n              batch: %i",
			   i,
			   pcp->count,
			   pcp->high,
			   pcp->batch);
#ifdef CONFIG_SMP
		pzstats = per_cpu_ptr(zone->per_cpu_zonestats, i);
		seq_printf(m, "\n  vm stats threshold: %d",
				pzstats->stat_threshold);
#endif
	}
	seq_printf(m,
		   "\n  node_unreclaimable:  %u"
		   "\n  start_pfn:           %lu",
		   pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES,
		   zone->zone_start_pfn);
	seq_putc(m, '\n');
}

该函数大致分下面几个部分剖析：

• 第一次调用时，输出当前 node 的内存统计信息，记录在 vm_node_stat 数组中，见 2.1 节；
• 输出 zone 的总信息，见 2.2 节；
• 输出 zone 的详细页面信息，记录在 zone->vm_stat 数组中，见 2.3 节；
• 输出 zone 的 pageset 信息，即zone 在每个 CPU 内存分配器信息，记录在 zone->pageset 链表中，见 2.4 节；
• 输出 zone 回收的 kswapd_failures 是否大于 MAX_RECLAIM_RETRIES(16) ，见 2.5节；
• 输出 zone 的start_pfn，见 2.5 节；

2.1 输出当前node的内存统计信息

Node 0, zone   Normal
  per-node stats
      nr_inactive_anon 122141
      nr_active_anon 58839
      nr_inactive_file 189638
      nr_active_file 208381
      nr_unevictable 26959
      nr_slab_reclaimable 23751
      nr_slab_unreclaimable 66678
      nr_isolated_anon 0
      nr_isolated_file 0
      workingset_nodes 9493
      workingset_refault_anon 233015
      workingset_refault_file 737280
      workingset_activate_anon 65319
      workingset_activate_file 283723
      workingset_restore_anon 20181
      workingset_restore_file 92763
      workingset_nodereclaim 3456
      nr_anon_pages 167321
      nr_mapped    113653
      nr_file_pages 467931
      nr_dirty     12
      nr_writeback 0
      nr_writeback_temp 0
      nr_shmem     12442
      nr_shmem_hugepages 0
      nr_shmem_pmdmapped 0
      nr_file_hugepages 0
      nr_file_pmdmapped 0
      nr_anon_transparent_hugepages 0
      nr_vmscan_write 398073
      nr_vmscan_immediate_reclaim 8683
      nr_dirtied   701230
      nr_written   1083923
      nr_kernel_misc_reclaimable 2752
      nr_foll_pin_acquired 0
      nr_foll_pin_released 0
      nr_kernel_stack 63056
      nr_shadow_call_stack 15792

参数解释：

2.2 输出zone的总信息

pages free     30498
        min      2048
        low      6047
        high     6559
        spanned  8381632
        present  930287
        managed  894377
        cma      38912
        protection: (0, 0, 0)

参数解释：

2.3 输出 zone 的详细页面信息

nr_free_pages 30498
      nr_zone_inactive_anon 122141
      nr_zone_active_anon 58839
      nr_zone_inactive_file 189638
      nr_zone_active_file 208381
      nr_zone_unevictable 26959
      nr_zone_write_pending 12
      nr_mlock     16525
      nr_page_table_pages 22903
      nr_bounce    0
      nr_zspages   53155
      nr_free_cma  0

2.4 输出 zone 的 pageset 信息

pagesets
    cpu: 0
              count: 87
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 1
              count: 112
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 2
              count: 355
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 3
              count: 49
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 4
              count: 0
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 5
              count: 24
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 6
              count: 353
              high:  378
              batch: 63
  vm stats threshold: 48
    cpu: 7
              count: 54
              high:  378
              batch: 63
  vm stats threshold: 48

参数解释：

2.5 其余信息

node_unreclaimable:  0
start_pfn:           525888

参数解释：