内核的system_state全局变量_内核模块有全局变量吗-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_43708235/article/details/125076135

本文详细介绍了Linux内核在启动过程中的状态变化，从SYSTEM_BOOTING到SYSTEM_RUNNING，并重点解析了build_all_zonelists函数如何根据系统状态进行不同的内存管理操作。在SYSTEM_BOOTING状态下，执行基础内存分配和初始化；而在其他状态，特别是运行态，涉及停止CPU以确保zonelist的安全构建。此外，还探讨了内存总量不足时关闭移动性分组的条件以及NUMA政策区的设置。

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内核一共分了五种状态，使用全局变量来进行区分内核的状态信息。
内核在开始时候为SYSTEM_BOOTING状态，在kernel_init函数中的init_post函数将system_state赋值为SYSTEM_RUNNING，在此后内核为运行态；

/include/linux/kernel.h
/* Values used for system_state */
extern enum system_states {
	SYSTEM_BOOTING,
	SYSTEM_RUNNING,
	SYSTEM_HALT,
	SYSTEM_POWER_OFF,
	SYSTEM_RESTART,
	SYSTEM_SUSPEND_DISK,
} system_state;

其中build_all_zonelists函数中，需要区分system_state的全局变量进行区分；

void __ref build_all_zonelists(void *data)
{
	set_zonelist_order();

	if (system_state == SYSTEM_BOOTING) {
		__build_all_zonelists(NULL);
		mminit_verify_zonelist();
		cpuset_init_current_mems_allowed();
	} else {
		/* we have to stop all cpus to guarantee there is no user
		   of zonelist */
#ifdef CONFIG_MEMORY_HOTPLUG
		if (data)
			setup_zone_pageset((struct zone *)data);
#endif
		stop_machine(__build_all_zonelists, NULL, NULL);
		/* 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",
			nr_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

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