The message “CPU 0/KVM invoked oom-killer” shows that the KVM subsystem on CPU 0 triggered the Out-of-Memory killer in the Linux kernel. At Bobcares, with our Server Management Service, we can handle your KVM issues.

What is “CPU 0/KVM invoked oom-killer?”

The breakdown of the issue “CPU 0/KVM invoked oom-killer” is as follows:

CPU 0 marks the system’s initial central processing unit (CPU) core. CPUs in multi-core systems have numbers that begin at 0. The CPU core that started the action appears in this section of the message.

Kernel-based Virtual Machine is KVM. The Linux kernel has a virtualization framework that enables the working of several VMs with separate resources on a single physical host.

OOM Killer Invoked means that the OOM Killer method was active. When the system runs out of memory and has to recover memory by ending processes to free up resources, it enables the Linux kernel’s OOM killer feature.

Here, the issue may be related to memory management, particularly with regards to Transparent Huge Pages (THP), ZFS dirty cache, and Apache’s memory usage. Let’s look into some of the quick fixes:

Fixes

1. Disabling THP can sometimes enhance performance and lower CPU usage, particularly during defragmentation. We need to consider if turning on THP is worth when comparing to the CPU savings from not needing to defragment them.

2. Even if it’s not used often, adding a swap device can help avoid OOM issues. This can be especially helpful when problems with memory overflow arise.

3. To improve memory management, we can cap the ZFS dirty cache at a smaller quantity.

4. Instead of using mpm_prefork with PHP as an Apache module, we can use modern web server setups like php-fpm with Nginx or Apache with mpm_event. This can enhance performance and give more insight into how PHP uses its resources.

5. Check the table sizes, query plans, and indexes in the MySQL database to find any possible problems. Make that buffer and memory-related settings for InnoDB storage engines are set correctly to maximize memory usage without causing out-of-memory issues.

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Conclusion

The article explains a brief note on the CPU 0/KVM invoked oom-killer issue, along with its solutions from our Support team.