某个机器看到一条日志:
Out of Memory: Kill process xxx (xxx) score 707 or sacrifice child
并且syslog, ssh等进程都被kill掉了.
简单了解了下OOM(Out of Memory)相关的问题
在Linux下，如果系统不足以分配程序申请的内存, OOM Killer就会被调用, 它会选择某个进程然后杀掉.
man 5 proc可以看到:
在Linux 2.6.11后, /proc/[pid]/oom_adj 可以控制oom的优先级等, 从-16到15, 数值越小, 被kill的可能性越低. 特殊值-17表示对当前进程禁用oom killer.
在Linux 2.6.36后, /proc/[pid]/oom_adj 被弃用了, 改为 /proc/[pid]/oom_score_adj, 值从-1000到1000, 越小被kill概率越小, -1000表示不被kill.
一般的进程 /proc/[pid]/oom_score_adj 值是0, 像ssh是-1000
关于vm.overcommit_memory, man 5 proc也可以看到:
/proc/sys/vm/overcommit_memory
This file contains the kernel virtual memory accounting mode. Values are:
0: heuristic overcommit (this is the default)
1: always overcommit, never check
2: always check, never overcommit
In mode 0, calls of mmap(2) with MAP_NORESERVE are not checked, and the default check is very weak, leading to the risk of getting a process "OOM-
killed". Under Linux 2.4, any nonzero value implies mode 1.
In mode 2 (available since Linux 2.6), the total virtual address space that can be allocated (CommitLimit in /proc/meminfo) is calculated as
CommitLimit = (total_RAM - total_huge_TLB) *
overcommit_ratio / 100 + total_swap
where:
* total_RAM is the total amount of RAM on the system;
* total_huge_TLB is the amount of memory set aside for huge pages;
* overcommit_ratio is the value in /proc/sys/vm/overcommit_ratio; and
* total_swap is the amount of swap space.
默认是0; 如果设置为2, 则不会出现nevercommit. 这个overcommit, 涉及到一个如上计算公式.
写了一个小程序用来耗尽内存:
$ more memtest.c
#include <stdio.h>
#include <stdlib.h>
int main() {
int *p;
while(1) {
int inc=10*sizeof(char);
p=(int*) calloc(1,inc);
*p = 123456;
if(!p) break;
}
}
默认情况下一会程序就被killed掉了, 如果设置另外一个进程的oom_score_adj为1000, 则这个进程先被杀掉.
当然, 还有问题，为何ssh等也都被杀掉了? 很奇葩