How to solve the overcommit_memory error in the redis database under Linux

Background

The company's redis sometimes fails to background save db. The following alarm is found through the log, which is probably caused by it:

[13223] 17 Mar 13:18:02.207 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1 ' for this to take effect.

So through searching, some people have encountered the same problem as me, and it is basically certain that it is caused by it.

Kernel parameter overcommit_memory

It is Memory allocation strategy

Optional values: 0, 1, 2.

• 0 means that the kernel will check whether there is enough available memory for the application process to use; if there is enough available memory, the memory application is allowed; otherwise, the memory application fails and an error is returned. to the application process.

• 1, indicates that the kernel allows all physical memory to be allocated regardless of the current memory status.

• 2, indicates that the kernel allows allocation of memory that exceeds the sum of all physical memory and swap space

What is Overcommit and OOM

Linux responds "yes" to most requests for memory so that it can run more and larger programs. Because after applying for memory, the memory will not be used immediately. This technique is called Overcommit. When Linux detects insufficient memory, it triggers the operation of the OOM killer (OOM stands for insufficient memory). In order to free up memory, it will give priority to killing some user-mode processes rather than kernel threads.

When oom-killer occurs, which processes will Linux choose to kill? The function that selects the process is the oom_badness function (in mm/oom_kill.c), which calculates the number of points (0~1000) for each process. The higher the score, the more likely the process is to be killed. The number of points per process is related to oom_score_adj, and oom_score_adj can be set (-1000 is the lowest, 1000 is the highest).

Solution:

It’s very simple, just follow the prompts (set vm.overcommit_memory to 1):

There are three ways to modify the kernel parameters, but you must have Root permissions:

• (1) Edit /etc/sysctl.conf, change vm.overcommit_memory=1, and then sysctl -p to make the configuration file take effect

• (2)sysctl vm.overcommit_memory=1

• (3)echo 1 > /proc/sys/vm/overcommit_memory

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