Docker -- WARNING: No swap limit support

Question

I'm running Docker(1.9.1) on Ubuntu 16.04. When I run docker info the last line of the output says WARNING: No swap limit support.

INFO[0781] GET /v1.21/info                              
Containers: 0
Images: 0
Server Version: 1.9.1
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 0
 Dirperm1 Supported: true
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 4.4.0-62-generic
Operating System: Ubuntu 16.04.1 LTS (containerized)
CPUs: 2
Total Memory: 3.664 GiB
Name: lenovo
ID: A3ZV:2EVK:U5QB:O7CG:PEDL:SANK:X74X:QNLC:VOTK:GFDR:S24T:C5KT
WARNING: No swap limit support

What does this warning mean? I definitely have a swap partition, as evidenced by free -mh though I don't understand why my swap has no entry under available

total        used        free      shared  buff/cache   available
Mem:           3.7G        1.9G        182M        157M        1.6G           1.3G
Swap:          3.8G        2.9M        3.8G

Answer 1

Swap limit support allows you to limit the swap the container uses, see https://docs.docker.com/engine/admin/resource_constraints

According to https://docs.docker.com/engine/installation/linux/linux-postinstall/#your-kernel-does-not-support-cgroup-swap-limit-capabilities :

You can enable these capabilities on Ubuntu or Debian by following these instructions. Memory and swap accounting incur an overhead of about 1% of the total available memory and a 10% overall performance degradation, even if Docker is not running.

1) Log into the Ubuntu or Debian host as a user with sudo privileges.

2) Edit the /etc/default/grub file. Add or edit the GRUB_CMDLINE_LINUX line to add the following two key-value pairs:

GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"

3) Update GRUB.

$ sudo update-grub

Answer 2

On my Google Cloud Compute instance I had to do it a little bit different than the accepted answer.

1) edit the file /etc/default/grub.d/50-cloudimg-settings.cfg

sudo nano /etc/default/grub.d/50-cloudimg-settings.cfg

1.1) modify or create the line

GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0 cgroup_enable=memory swapaccount=1"

1.2) save

2) update grup

sudo update-grub

3) reboot

sudo reboot