linux环境下查看因内存占用过大被杀掉的进程-Toy模板网

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前言

最近发生两次游戏服务器进程突然消失的事件，查询日志上下文没有找到有用的信息，日志显示运行到某处戛然而止，此处代码逻辑简单，排除异常逻辑导致的服务器进程崩溃，所以联想到之前同一台服务器上部署多个进程，因占用内存太大被内核杀死的情况，猜测本次也是这个原因。

查询方法

通过搜索引擎找到了两种查询方法，一种是直接过滤系统日志，一种是借助 dmesg 命令，备注以下命令在 CentOS 7 上测试通过

通过系统日志查找

[root@demo]# grep "Out of memory" /var/log/messages
Apr  4 10:32:30 hk-dev kernel: Out of memory: Kill process 2434 (Game9) score 212 or sacrifice child
Apr  4 10:33:53 hk-dev kernel: Out of memory: Kill process 2476 (git) score 381 or sacrifice child
Apr  4 10:33:53 hk-dev kernel: Out of memory: Kill process 2777 (git) score 381 or sacrifice child

通过dmesg命令查找

[root@demo]# dmesg -T | grep "Out of memory"
[Mon Aug 30 12:06:25 2021] Out of memory: Kill process 22437 (git) score 400 or sacrifice child
[Wed Sep 22 20:23:52 2021] Out of memory: Kill process 29780 (Game6) score 161 or sacrifice child
[Wed Mar 29 15:54:31 2023] Out of memory: Kill process 29093 (git) score 388 or sacrifice child
[Tue Apr  4 10:24:05 2023] Out of memory: Kill process 2434 (Game9) score 212 or sacrifice child
[Tue Apr  4 10:25:29 2023] Out of memory: Kill process 2476 (git) score 381 or sacrifice child

进程被杀的原因

Linux 内核有个机制叫OOM killer，全称为 Out Of Memory killer，很形象的一个名字——内存溢出杀手，这个机制会监控那些占用内存过大，尤其是瞬间占用内存很快的进程，为防止机器内存耗尽而主动把该进程杀掉。

当内核检测到系统内存不足、挑选并杀掉某个进程的过程可以参考内核源代码 linux/mm/oom_kill.c（2023-4-4 23:24:07确认了此文件存在），当系统内存不足的时候，out_of_memory() 函数被触发，然后调用 select_bad_process() 函数选择一个进程杀掉，这个选择的过程是通过调用 oom_badness() 函数实现的，挑选的算法和想法都暴力但朴实：就是找到最占用内存的进程。

源码如下:

/**
 * oom_badness - heuristic function to determine which candidate task to kill
 * @p: task struct of which task we should calculate
 * @totalpages: total present RAM allowed for page allocation
 *
 * The heuristic for determining which task to kill is made to be as simple and
 * predictable as possible.  The goal is to return the highest value for the
 * task consuming the most memory to avoid subsequent oom failures.
 */
long oom_badness(struct task_struct *p, unsigned long totalpages)
{
	long points;
	long adj;

	if (oom_unkillable_task(p))
		return LONG_MIN;

	p = find_lock_task_mm(p);
	if (!p)
		return LONG_MIN;

	/*
	 * Do not even consider tasks which are explicitly marked oom
	 * unkillable or have been already oom reaped or the are in
	 * the middle of vfork
	 */
	adj = (long)p->signal->oom_score_adj;
	if (adj == OOM_SCORE_ADJ_MIN ||
			test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
			in_vfork(p)) {
		task_unlock(p);
		return LONG_MIN;
	}

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
		mm_pgtables_bytes(p->mm) / PAGE_SIZE;
	task_unlock(p);

	/* Normalize to oom_score_adj units */
	adj *= totalpages / 1000;
	points += adj;

	return points;
}