KSM in Proxmox VE
KSM in Proxmox VE is primarily designed for QEMU/KVM virtual machines (VMs). It does not provide meaningful deduplication benefits for LXC containers, because containers share the host kernel and libraries directly rather than duplicating them in isolated memory spaces pve.proxmox.com.
🔍 Why KSM is VM-focused
- VMs (QEMU/KVM):
- Each VM runs its own kernel and userland, often duplicating identical memory pages (e.g., multiple Linux guests with the same libraries).
- KSM scans guest memory and merges identical pages, reducing physical RAM usage.
- Proxmox even allows enabling/disabling KSM per-VM (
qm set <vmid> --allow-ksm 0) pve.proxmox.com.
- LXC Containers:
- Containers share the same host kernel and often the same libraries through the filesystem.
- Memory pages are not duplicated in the same way as VMs, so KSM has little to merge.
- Deduplication is effectively redundant because processes inside LXC already benefit from the host’s natural memory sharing (e.g., shared libraries mapped once into memory).
⚖️ Comparison Table
| Feature | VMs (QEMU/KVM) | LXC Containers |
|---|---|---|
| Kernel isolation | Each VM has its own kernel | Shared host kernel |
| Memory duplication | High (multiple OS instances) | Low (shared libraries, kernel) |
| KSM effectiveness | Significant savings possible | Minimal to none |
| Security considerations | Risk of side-channel attacks between VMs | Less relevant (same kernel space) |
| Control granularity | Can enable/disable per VM | No per-container KSM toggle |
🚨 Risks & Considerations
- Security: KSM can expose VMs to side-channel attacks, since merged pages can leak timing information between guests pve.proxmox.com.
- Hosting environments: If you run multi-tenant VMs, disabling KSM may be required by regulation or best practice.
- Containers: Since LXC doesn’t duplicate kernel memory, enabling/disabling KSM has negligible impact.
âś… Bottom line for Proxmox:
KSM is useful for VMs only. For LXC containers, it doesn’t add value because containers already share memory at the process/kernel level. If your workload is container-heavy, you can safely ignore KSM tuning—it won’t make a difference.
#enoughsaid