Quota groups

A quota group sets resource limits on services inside the snaps it contains. Currently, maximum memory and CPU usage are supported as resource limits.

Quota groups are created, removed and queried with the following snap commands:

  • set-quota: create or update a quota group
  • quota: show quota group for a set of snaps
  • quotas: show all quota groups
  • remove-quota: remove a quota group

Quota groups require snap version 2.52 and they’re currently considered experimental. To experiment with quota groups, an experimental feature-flag must be first enabled:

$ sudo snap set system experimental.quota-groups=true

Creating a quota group

To create a quota group, use the set-quota command with a group name as an argument and either --memory=<amount> to set a maximum memory resource limit, or --cpu=<amount> to set a maximum CPU resource limit. Snaps with services can optionally be listed to include them within the quota group.

See below for more specific details on memory limits and CPU limits.

Memory limits

Memory units can be ‘B’, ‘KB’, 'MB or ‘GB’ with a size greater than 4KB:

$ sudo snap set-quota highmem --memory=2GB

The memory limit for a quota group can only be increased. Increasing the memory limit for a quota group does not restart any services associated with snaps in the quota group.

To decrease the memory limit for a quota group, the entire group must be removed with the remove-quota command and recreated with a lower limit.

CPU limits

CPU limits can be set in 4 different ways, some of which can be combined depending on requirements:

  1. Percentage of total CPU resources
  2. Percentage of a given number of CPU cores
  3. Percentage for specific cores
  4. Limit the number of threads

Without a specified CPU limit, all quota groups can use the full system capacity.

1. Percentage of total CPU resources

--cpu=<percentage>%

Sets a relative percentage limit on how much execution time a process receives, regardless of the number of cores available, up to 100%.

2. Percentage of a given number of CPU cores

--cpu=<number of cores>x<percentage>%**

One or more cores can be specified alongside a CPU percentage to allocate relative CPU resources across only that number of cores.

For example, --cpu=2x100% on a 4 core system would permit a process to run at full capacity on only two cores, which is equivalent to 50% of full system capacity.

3. Percentage for specific cores

--cpu-set=<core number 1>,<core number 2> --cpu=<percentage>%

Using an additional --cpu-set argument with --cpu , it’s possible to specify exactly which cores to be used as the CPU resources for that quote group.

For example, --cpu-set=0,1 --cpu=100% will permit up to 100% CPU resource usage on 2 specific cores (0 and 1).

The following example will allow up to a maximum of half usage combined on four specific cores which means the sum of usage across all 4 specific cores cannot exceed 200%:

$ snap set-quota max-two-specific-cores --cpu-set=0,1,2,3 --cpu=50%

In the above example, services in the max-two-specific-cores quota group could run using 100% of two cores and 0% of the other two cores, or 25% of each core, 33% of 3 of the cores and 0% of the last core, or any other combination that does not exceed 200%. The number 200% comes from the size of the --cpu-set set multiplied by the --cpu setting.

4. Limit the number of threads

--threads=<thread limit

The --threads option is used to limit the number of threads or processes that can be created by the snaps within the quota group.

For example, --threads=4096 will limit a quota group to no more than 4096 threads or processes.

The threads option can also be used with both --cpu and --cpu-set options to target specific requirements:

$ snap set-quota max-two-specific-cores --cpu-set=0,1,2,3 --cpu=50% --threads=8092

By default, quota groups are not limited in the number of threads they can create.

Viewing quotas

If the group already exists, set-quota will update its resource limits.

Use the quotas command to view created quota groups:

$ snap quotas
Quota      Parent  Constraints                        Current
highmem            memory=2.00GB cpu=50%,cpu-set=0,1
cpuhalf            cpu=50%,cpu-set=0,1
manycores          cpu=2x,cpu=100%,threads=4096
maxcores           cpu=100%
memcpu             memory=2.00GB,cpu=50%
threads            threads=4096

Snaps can belong to only one quota group, but quota groups can be nested.

Nested quota groups

To create a nested quota group, add the --parent=<parent group> argument to the set-quota command when creating a new quota group:

$ sudo snap set-quota lowmem --memory=1GB --parent=highmem

The quotas command will also show nested quota groups:

$ snap quotas
Quota    Parent   Constraints    Current
highmem           memory=2.00GB  
lowmem   highmem  memory=1.00GB  

The total resource use of nested quota groups cannot exceed that of the parent group.

Updating a quota group

Add the names of one or more snaps to the set-quota command to include those snaps in the quota group when its created:

$ sudo snap set-quota lowmem go-example-webserver --parent=highmem

If the quota group already exists, snaps can be added by using set-quota without the resource limit:

$ sudo snap set-quota lowmem go-example-webserver

Adding new a snap to a quota group will result in all non-disabled services in that snap being restarted.

New quotas can be set on existing quota groups, but existing quotas cannot be removed from a quota group, without removing and recreating the entire group.

The CPU set limit for a quota group can be modified to include new cores, or to remove existing cores from the quota already set.

The threads limit for a quota group can be increased but not decreased. To decrease the threads limit for a quota group, the entire group must be removed with the remove-quota command and recreated with a lower limit.

Group members and resource usage

The quota command shows information about a quota group, including the set of snaps it includes and any subgroups it contains, as well as its resource constraints and the current usage of those constrained resources by snap services in those snaps:

$ snap quota lowmem
name:    lowmem
parent:  highmem
constraints:
  memory:  1.00GB
current:
  memory:  5.32MB
snaps:
  - go-example-webserver

Use the quota command on the parent of any nested groups to view total resource usage and subgroups:

$ snap quota highmem
name:  highmem
constraints:
  memory:  2.00GB
current:
  memory:  5.35MB
subgroups:
  - lowmem

Removing snaps and quota groups

To remove a snap from a quota group, the entire group must be removed with the remove-quota command and the quota group recreated without the snaps:

$ sudo snap remove-quota lowmem
$ sudo snap set-quota lowmem --memory=1GB
$ snap quota lowmem
name:  lowmem
constraints:
  memory:  1.00GB
current:
  memory:  0B

Currently, only quota groups with no subgroups can be removed. In order to remove a quota group with subgroups, the subgroups must be first removed until there are no further subgroups in the group, then the group itself can be removed.

An existing subgroup cannot be moved from one parent to another.

To remove a subgroup from a quota group, the subgroup must be first removed directly with the remove-quota command.


Last updated 20 days ago.