初始化内存管理区列表详解-优快云博客

本文链接：https://blog.youkuaiyun.com/yunsongice/article/details/6171320

本文介绍了Linux内核启动过程中的内存管理区初始化，重点解析了start_kernel函数中调用的build_all_zonelists()函数，以及如何通过for_each_online_node循环和build_zonelists函数来构建内存管理区列表。同时提到了build_zonelist_cache函数在初始化内存管理区缓存的作用。

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5.4 初始化内存管理区列表

回到start_kernel函数，569行的build_all_zonelists()函数，来自mm/page_alloc.c：

2815void build_all_zonelists(void)

2816{

2817 set_zonelist_order();

2818

2819 if (system_state == SYSTEM_BOOTING) {

2820 __build_all_zonelists(NULL);

2821 mminit_verify_zonelist();

2822 cpuset_init_current_mems_allowed();

2823 } else {

2824 /* we have to stop all cpus to guarantee there is no user

2825 of zonelist */

2826 stop_machine(__build_all_zonelists, NULL, NULL);

2827 /* cpuset refresh routine should be here */

2828 }

2829 vm_total_pages = nr_free_pagecache_pages();

2830 /* ……一大堆注释*/

2837 if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES))

2838 page_group_by_mobility_disabled = 1;

2839 else

2840 page_group_by_mobility_disabled = 0;

2841

2842 printk("Built %i zonelists in %s order, mobility grouping %s. "

2843 "Total pages: %ld/n",

2844 nr_online_nodes,

2845 zonelist_order_name[current_zonelist_order],

2846 page_group_by_mobility_disabled ? "off" : "on",

2847 vm_total_pages);

2848#ifdef CONFIG_NUMA

2849 printk("Policy zone: %s/n", zone_names[policy_zone]);

2850#endif

2851}

其本质上调用__build_all_zonelists(NULL)：

2780/* return values int ....just for stop_machine() */

2781static int __build_all_zonelists(void *dummy)

2782{

2783 int nid;

2784 int cpu;

2785

2786#ifdef CONFIG_NUMA

2787 memset(node_load, 0, sizeof(node_load));

2788#endif

2789 for_each_online_node(nid) {

2790 pg_data_t *pgdat = NODE_DATA(nid);

2791

2792 build_zonelists(pgdat);

2793 build_zonelist_cache(pgdat);

2794 }

2795

2796 /* ……一大堆注释*/

2809 for_each_possible_cpu(cpu)

2810 setup_pageset(&per_cpu(boot_pageset, cpu), 0);

2811

2812 return 0;

2813}

2789行，for_each_online_node我们很熟悉了，只执行一次的循环。2790行是最著名的pg_data_t，就是NODE_DATA(0)的那个结构。随后执行build_zonelists函数：

2637static void build_zonelists(pg_data_t *pgdat)

2638{

2639 int j, node, load;

2640 enum zone_type i;

2641 nodemask_t used_mask;

2642 int local_node, prev_node;

2643 struct zonelist *zonelist;

2644 int order = current_zonelist_order;

2645

2646 /* initialize zonelists */

2647 for (i = 0; i < MAX_ZONELISTS; i++) {

2648 zonelist = pgdat->node_zonelists + i;

2649 zonelist->_zonerefs[0].zone = NULL;

2650 zonelist->_zonerefs[0].zone_idx = 0;

2651 }

2652

2653 /* NUMA-aware ordering of nodes */

2654 local_node = pgdat->node_id;

2655 load = nr_online_nodes;

2656 prev_node = local_node;

2657 nodes_clear(used_mask);

2658

2659 memset(node_order, 0, sizeof(node_order));

2660 j = 0;

2661

2662 while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {

2663 int distance = node_distance(local_node, node);

2664

2665 /*

2666 * If another node is sufficiently far away then it is better

2667 * to reclaim pages in a zone before going off node.

2668 */

2669 if (distance > RECLAIM_DISTANCE)

2670 zone_reclaim_mode = 1;

2671

2672 /*

2673 * We don't want to pressure a particular node.

2674 * So adding penalty to the first node in same

2675 * distance group to make it round-robin.

2676 */

2677 if (distance != node_distance(local_node, prev_node))

2678 node_load[node] = load;

2679

2680 prev_node = node;

2681 load--;

2682 if (order == ZONELIST_ORDER_NODE)

2683 build_zonelists_in_node_order(pgdat, node);

2684 else

2685 node_order[j++] = node; /* remember order */

2686 }

2687

2688 if (order == ZONELIST_ORDER_ZONE) {

2689 /* calculate node order -- i.e., DMA last! */

2690 build_zonelists_in_zone_order(pgdat, j);

2691 }

2692

2693 build_thisnode_zonelists(pgdat);

2694}

build_zonelists函数2647-2651初始化NODE_DATA(0)的node_zonelist字段。我们继续走：

2697static void build_zonelist_cache(pg_data_t *pgdat)

2698{

2699 struct zonelist *zonelist;

2700 struct zonelist_cache *zlc;

2701 struct zoneref *z;

2702

2703 zonelist = &pgdat->node_zonelists[0];

2704 zonelist->zlcache_ptr = zlc = &zonelist->zlcache;

2705 bitmap_zero(zlc->fullzones, MAX_ZONES_PER_ZONELIST);

2706 for (z = zonelist->_zonerefs; z->zone; z++)

2707 zlc->z_to_n[z - zonelist->_zonerefs] = zonelist_node_idx(z);

2708}

build_zonelist_cache函数初始化内存管理区的缓存，我这里就不深入下去了。回到build_all_zonelists()函数中，略去调试的代码，以及设置几个关于zone的策略的全局变量的代码，该函数就结束了。