Swappiness 1 on a small RAM VM in Proxmox stops the constant small MiB swap writes, but it also makes the OOM killer jump in sooner when memory gets tight. If you’re seeing swap I/O on a 1-2GB VM, the fix is usually adding RAM or tuning the app, not just cranking swappiness down.
What swappiness actually does
Swappiness is a kernel tunable from 0 to 100. Lower values tell the kernel to avoid swapping unless it absolutely has to. On a desktop with 32GB RAM, setting it to 10 is fine. On a VM with 1GB RAM, it’s a different story.
With swappiness=1, the kernel will hold onto page cache and anonymous memory until the last moment. That means less disk I/O from swapping, but when memory runs out, the OOM killer has to pick a process to kill. And on a small VM, that moment comes fast.
What I measured on PVE 9
I tested a Debian 12 VM with 1GB RAM on Proxmox VE 9. Running a typical LAMP stack with MySQL and Apache, default swappiness (60) caused constant swap writes of a few MiB every few seconds. The disk was busy, and the VM felt sluggish.
Setting vm.swappiness=1 in /etc/sysctl.conf stopped the swap writes almost entirely. But under load, the OOM killer started killing MySQL or Apache within minutes. The VM didn’t slow down gradually—it just died.
The real tradeoff
Swappiness=1 is not a memory-saving trick. It’s a swap avoidance trick. If your VM has enough RAM for its workload, it’s fine. If it doesn’t, you’re just moving the pain from slow disk I/O to sudden process kills.
For a small RAM VM, I’d rather see swappiness at 10 or 20. That still reduces swap I/O but gives the kernel a bit of room to breathe. Or better, add more RAM. A 512MB bump is cheaper than debugging random OOM kills at 3am.
When swappiness=1 makes sense
If your VM is running a single-purpose app that never spikes memory, swappiness=1 is fine. A DNS server or a lightweight proxy won’t notice. But if you’re running a database or anything that can grow, leave it higher.
Check your current swappiness with cat /proc/sys/vm/swappiness. If it’s already low and you still see swap I/O, your VM is simply out of RAM. No sysctl will fix that.
Related
If you’re tuning a Proxmox VM, also check memory ballooning doesn’t reduce host RAM usage? Here’s why and the fix.
