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Why is my home server using so much RAM for cache + buffer? (lemmy.dbzer0.com)

submitted 3 hours ago by A9nWGzYt@lemmy.dbzer0.com to c/selfhosted@lemmy.world

12 comments fedilink hide all child comments

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)

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[–] eager_eagle@lemmy.world 1 points 1 hour ago* (last edited 1 hour ago)

No point in messing with swappiness settings, trust me. You want to address the reason this happens in the first place, not disable to reduce swap.

I've had a nearly identical scenario at work. The reason? A data verification process that went through 100s of thousands of files to run their checksums and check integrity. This was working as intended, but the system alerts were firing because of that high buffer/cache utilization. So check which processes have highest IO and you might find the answer. Swap is just a side effect.