I have noticed that my home server is strangely using lots of swap (~5 GB), despite having only a few lightweight processes running and loads of RAM installed (32 GB).
Upon configuring Grafana + Prometheus, I noticed a trend where cache + buffer will progressively increase until swap starts to be used. My system and services combined will use ~8 GB RAM. Upon rebooting, the cache + buffer will start anywhere from 3–10 GB, progressively ramp up to ~25 GB in 1–2h, where swap will start to be needed (~3 GB). See the image attached for reference.
My swap filesystem is on an expensive (to me) SSD, and I would like to reduce its wear by as much as possible. I understand that swap can introduce only minimal wear on SSDs depending on its nature and that it can be harmless, but I am still not sure what is causing this behavior (and why) and whether I should worry about it or not. So I figured I should investigate what is happening here.
My main question is, how can I figure out what is causing this behavior? Is it expected? I am looking for guidance from others who are more experienced than me in the topic.
A little bit about my system:
I am running Debian 12 on an NVMe SSD containing the root partition (btrfs) and docker services. I also have two HDDs, one with persistent data (ext4), and the other with backups (ext4). This is majoritarily a single-user machine. I tried using the following kernel parameters, but it hasn’t helped:
vm.swappiness=10
vm.vfs_cache_pressure=200
My docker services are:
- *arr stack
- jellyfin
- nextcloud
- immich
- open-webui + ollama
- pi-hole
- invidious
- romm
- nginx proxy manager
- grafana + prometheus
- other minor services that I don’t think are doing much (uptime-kuma, stirlingpdf, vaultwarden, etc)
https://www.linuxatemyram.com/
This is normal. Linux caches disk reads so that you don’t have to go to her/SSD to reread blocks. If your app isn’t using the ram Linux will use it instead.
Zero reason to be concerned, because if your app allocates more memory Linux will evict the cached pages to make sure your apps have plenty of space.
In this case your apps have memory that isn’t being touched (sometimes a sign of a memory leak), and Linux has decided that caching your disk access is more advantageous than keeping the unused application memory in ram.
If you have apps that you don’t use often and are really slow to access when you finally do, keep lowering that swappiness value or just remove swap all together if it annoys you.
Looking at your graph you have a lot of ram that you don’t really need… I would just disable swap entirely. Otherwise you are just wasting write cycles on your SSD.