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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

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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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[–] non_burglar@lemmy.world 4 points 1 hour ago

I agree that hitting swap is not ideal, but messing with swappiness sysctl is almost never the answer and very often leads to more problems than it solves.

If you want to tune for workload without needing fairly deep understanding of how Linux manages memory, use a sysctl that sets a whole system behaviour like CPU governor presets.

IMO, Linux is configured for “old” systems by default: slow HDDs, and constrained RAM pools, where disk IO really, really needs caching, and where idle background processes take a large fraction of RAM.

Not really a matter of opinion, and not true since kernel 5.1 when ssds became first class citizens.