全局启动函数start_kernel函数注解

asmlinkage void __init start_kernel(void)
{
	char * command_line;
	extern struct kernel_param __start___param[], __stop___param[];

	smp_setup_processor_id();

	/*
	 * Need to run as early as possible, to initialize the
	 * lockdep hash:
	 */
	unwind_init();
	lockdep_init();
	cgroup_init_early();

	local_irq_disable();
	early_boot_irqs_off();
	early_init_irq_lock_class();

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
	lock_kernel();
	tick_init();
	boot_cpu_init();
	page_address_init();
	printk(KERN_NOTICE);
	printk(linux_banner);
	setup_arch(&command_line);
	setup_command_line(command_line);
	unwind_setup();
	setup_per_cpu_areas();
	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */

	/*
	 * Set up the scheduler prior starting any interrupts (such as the
	 * timer interrupt). Full topology setup happens at smp_init()
	 * time - but meanwhile we still have a functioning scheduler.
	 */
	sched_init();
	/*
	 * Disable preemption - early bootup scheduling is extremely
	 * fragile until we cpu_idle() for the first time.
	 */
	preempt_disable();
	build_all_zonelists();
	page_alloc_init();
	printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
	parse_early_param();
	parse_args("Booting kernel", static_command_line, __start___param,
		   __stop___param - __start___param,
		   &unknown_bootoption);
	if (!irqs_disabled()) {
		printk(KERN_WARNING "start_kernel(): bug: interrupts were "
				"enabled *very* early, fixing it\n");
		local_irq_disable();
	}
	sort_main_extable();
	trap_init();
	rcu_init();
	init_IRQ();
	pidhash_init();
	init_timers();
	hrtimers_init();
	softirq_init();
	timekeeping_init();
	time_init();
	profile_init();
	if (!irqs_disabled())
		printk("start_kernel(): bug: interrupts were enabled early\n");
	early_boot_irqs_on();
	local_irq_enable();

	/*
	 * HACK ALERT! This is early. We're enabling the console before
	 * we've done PCI setups etc, and console_init() must be aware of
	 * this. But we do want output early, in case something goes wrong.
	 */
	console_init();
	if (panic_later)
		panic(panic_later, panic_param);

	lockdep_info();

	/*
	 * Need to run this when irqs are enabled, because it wants
	 * to self-test [hard/soft]-irqs on/off lock inversion bugs
	 * too:
	 */
	locking_selftest();

#ifdef CONFIG_BLK_DEV_INITRD
	if (initrd_start && !initrd_below_start_ok &&
			initrd_start < min_low_pfn << PAGE_SHIFT) {
		printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
		    "disabling it.\n",initrd_start,min_low_pfn << PAGE_SHIFT);
		initrd_start = 0;
	}
#endif
	vfs_caches_init_early();
	cpuset_init_early();
	mem_init();
	kmem_cache_init();
	setup_per_cpu_pageset();
	numa_policy_init();
	if (late_time_init)
		late_time_init();
	calibrate_delay();
	pidmap_init();
	pgtable_cache_init();
	prio_tree_init();
	anon_vma_init();
#ifdef CONFIG_X86
	if (efi_enabled)
		efi_enter_virtual_mode();
#endif
	fork_init(num_physpages);
	proc_caches_init();
	buffer_init();
	unnamed_dev_init();
	key_init();
	security_init();
	vfs_caches_init(num_physpages);
	radix_tree_init();
	signals_init();
	/* rootfs populating might need page-writeback */
	page_writeback_init();
#ifdef CONFIG_PROC_FS
	proc_root_init();
#endif
	cgroup_init();
	cpuset_init();
	taskstats_init_early();
	delayacct_init();

	check_bugs();

	acpi_early_init(); /* before LAPIC and SMP init */

	/* Do the rest non-__init'ed, we're now alive */
	rest_init();
}

2、build_all_zonelist用来建立管理结点以及其他内存区域所需的数据结构。其中主要工作由__build_all_zonelist来完成。

/* return values int ....just for stop_machine_run() */
static int __build_all_zonelists(void *dummy)
{
	int nid;//for_each_online_node遍历了系统中所有活动的结点
	for_each_online_node(nid) {
		//NODE_DATA宏，用于通过结点编号来查询与一个NUMA结点相关的pgdata_t实例
		pg_data_t *pgdat = NODE_DATA(nid);

		build_zonelists(pgdat);
		build_zonelist_cache(pgdat);
	}
	return 0;
}

void build_all_zonelists(void)
{
	set_zonelist_order();

	if (system_state == SYSTEM_BOOTING) {
		__build_all_zonelists(NULL);
		cpuset_init_current_mems_allowed();
	} else {
		/* we have to stop all cpus to guarantee there is no user
		   of zonelist */
		stop_machine_run(__build_all_zonelists, NULL, NR_CPUS);
		/* cpuset refresh routine should be here */
	}
	vm_total_pages = nr_free_pagecache_pages();
	/*
	 * Disable grouping by mobility if the number of pages in the
	 * system is too low to allow the mechanism to work. It would be
	 * more accurate, but expensive to check per-zone. This check is
	 * made on memory-hotadd so a system can start with mobility
	 * disabled and enable it later
	 */
	if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES))
		page_group_by_mobility_disabled = 1;
	else
		page_group_by_mobility_disabled = 0;

	printk("Built %i zonelists in %s order, mobility grouping %s.  "
		"Total pages: %ld\n",
			num_online_nodes(),
			zonelist_order_name[current_zonelist_order],
			page_group_by_mobility_disabled ? "off" : "on",
			vm_total_pages);
#ifdef CONFIG_NUMA
	printk("Policy zone: %s\n", zone_names[policy_zone]);
#endif
}

3、NODE_DATA，用来根据结点编号，查询一个NUMA结点相关的pgdata_t实例

在UMA系统上，NODE_DATA返回contig_page_data的地址。

绝大多数的实现是：

<mmzone.h>

#define NODE_DATA(nid)		(&contig_page_data)