It looks to me like the WSL2 container docker-desktop is using 12 GB RAM to run one container with 24 MB RAM. What gives? (details below).
Also, when I add up all the resident RAM (VSZ) from all the processes in docker-desktop, the total is only 4687251 KB or 4.4 GB, so where did the remaining 7 GB RAM go?
I tried restarting Docker Desktop from the taskbar and I tried terminating the docker-desktop WSL2 container (with wsl.exec -t), both of which made no difference. I rebooted the entire Windows machine and now it uses a much more reasonable 2GB RAM. Which is still kind of a lot compared to my Ubuntu 20.04 WSL2 that uses 595MB RAM.
So: Why is docker-desktop using 12GB RAM to serve a tiny container? Can I fix that without rebooting the entire machine?
# What is docker-desktop-data? It doesn't support any commands...
$ wsl.exe -d docker-desktop-data free -m
# docker-desktop is using approx 12 GB RAM
$ wsl.exe -d docker-desktop free -m
total used free shared buffers cached
Mem: 25510 12245 13264 399 1461 8191
-/+ buffers/cache: 2592 22917
Swap: 7168 2 7165
# but docker containers are only using 24 MB?
$ docker stats --no-stream
CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
2f29ebe21db3 gitlab-runner 0.04% 24.55MiB / 24.91GiB 0.10% 7.49MB / 18MB 0B / 0B 30
# Sort by and sum up the VSZ values from ps in the dockerdesktop container
$ wsl.exe -d docker-desktop ps -o pid,user,vsz,rss,comm,args | perl -ane '$mem = $F[2]; $mem = $1 * 1024 if $mem =~ /(.*)m$/; printf "%9s $_", $mem; $totmem += $mem ; END { printf "Totmem: %10d\n", $totmem }' | sort | tail -n 10
113664 259 root 111m 14m containerd-shim /usr/bin/containerd-shim-runc-v2 -namespace services.linuxkit -id docker -address /run/containerd/containerd.sock
113664 418 root 111m 13m containerd-shim /usr/bin/containerd-shim-runc-v2 -namespace services.linuxkit -id socks -address /run/containerd/containerd.sock
113664 493 root 111m 13m containerd-shim /usr/bin/containerd-shim-runc-v2 -namespace services.linuxkit -id vpnkit-forwarder -address /run/containerd/containerd.sock
145408 1119 root 142m 36m gitlab-runner gitlab-runner run --user=gitlab-runner --working-directory=/home/gitlab-runner
150528 176 root 147m 41m containerd /usr/bin/containerd
712704 26 root 696m 20m vpnkit-bridge /usr/bin/vpnkit-bridge --pid-file=/run/vpnkit-bridge.pid --addr=stdio guest
723968 16 root 707m 25m wsl-bootstrap wsl-bootstrap run --base-image /mnt/host/c/Program Files/Docker/Docker/resources/wsl/docker-for-wsl.iso --version-pack /mnt/host/c/Program Files/Docker/Docker/resources/docker.tar --cli-iso /mnt/host/c/Program Files/Docker/Docker/resources/wsl/docker-wsl-cli.iso
729088 234 root 712m 30m diagnosticsd /usr/local/bin/diagnosticsd
730112 316 root 713m 31m lifecycle-serve /usr/bin/lifecycle-server
Totmem: 4687251
Take a look at WSL2 configuration file documented here:
https://learn.microsoft.com/en-us/windows/wsl/wsl-config#configure-global-options-with-wslconfig
You can limit usage of WSL engine to let say 3GB and 2vCPU by creating %userprofile%\.wslconfig file as follow:
[wsl2]
memory=3GB
processors=2
As I understand the memory is shared between all WSL namespaces/distros and what are you seeing typing free is memory occupied mostly by file cache in your other distros.
To quickly and in a dirty way free up your RAM you execute as root sync; echo 3 > /proc/sys/vm/drop_caches in any of your WSL2 distros.
According to docker-desktop-data HERE you can check answer, simply it is backing storage for your containers