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Proxmox KSM Sharing | All About

Memory management plays a key role in making sure that resources are utilized optimally while maintaining security and performance. One such technique is KSM.

KSM, short for Kernel Samepage Merging is an optional memory deduplication feature. It is offered by the Linux kernel. Furthermore, it is enabled by default in Proxmox VE.

Today, we are going to take a look at what KSM is and how it works.

What is KSM?

KSM is a memory optimization feature available in the Linux kernel. It is popular for its role in Proxmox VE. It’s primary function is to identify and combine identical memory content to reduce redundancy and improve memory utilization.

In other words, KSM scans a certain range of physical memory pages to identify those containing identical content. Once identified, it locates the corresponding virtual pages mapped to those physical pages.

Then, these virtual pages are remapped to point to a single physical page, thereby consolidating the memory. The original pages are then released. Additionally, these virtual pages are marked as “copy-on-write”. This ensures that any write operations create a new memory area, preserving the shared physical page.

Benefits of KSM

A key benefit of KSM is that it helps optimize memory usage in virtualization environments. When multiple VMs are running similar OS or workloads, they often share common memory pages.

KSM recognizes these pages and merges them, hence reducing memory redundancy and freeing up resources.

How to disable KSM

However, KSM can expose VMs to side-channel attacks. We can easily disable KSM to boost security with these steps:

1. First, we have to check if KSM is active with this command:

   systemctl status ksmtuned
2. At this point, if KSM is active, we can disable it as seen here:

   systemctl disable --now ksmtuned
3. Furthermore, we can unmerge all currently merged pages with this command:

   echo 2 > /sys/kernel/mm/ksm/run

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Conclusion

In summary, our Support Techs introduced us to Proxmox KSM Sharing and demonstrated how to disable it.