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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
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1 Answer 1

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8

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

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2 Comments

Fantastic! You're right... It is sneaky though. The total of (used+buffers) seems to be similar in all the WSL distributions (how could they call them "distributions"?), but what in one was a little used RAM and lots of buffers in another was shown as lots of used RAM. Go figure. But yes, this was the piece I was missing: The memory is shared. (I don't want to limit it, though...)
Yeah def seems like a docker-desktop bug if they're reporting full WSL2 ram usage vs. just what docker is using as it claims.

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