defaults: drop setting generator for hugepages

[ytsssun]

Issue number:

Relevant #4385

Description of changes:
Drop setting generator for hugepages.

Testing done:

1. Build a test AMI and launch with userdata

[settings.kernel.sysctl]
"vm.nr_hugepages" = "3000"

Verified that no hugepages settings got generated for “vm/nr_hugepages”

bash-5.1# apiclient get settings.kernel
{
  "settings": {
    "kernel": {
      "lockdown": "integrity",
      "sysctl": {
        "vm.nr_hugepages": "3000"
      }
    }
  }
}

The hugepages value is honored

bash-5.1# cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
3000

Settings generator not showing up - no entry ("vm/nr_hugepages") found in the setting generators.

2. Build a 1.33.0 AMI and confirm the existing behavior

[settings.updates]
metadata-base-url = "$METADATA_BASE_URL"
targets-base-url ="$TARGETS_BASE_URL"
ignore-waves = true
 
[settings.host-containers.admin]
enabled = true

[settings.kernel.sysctl]
"vm.nr_hugepages" = "3000"

See that the setting generator generates the extra entry “vm/nr_hugepages”

bash-5.1# apiclient get settings.kernel
{
  "settings": {
    "kernel": {
      "lockdown": "integrity",
      "sysctl": {
        "vm.nr_hugepages": "3000",
        "vm/nr_hugepages": "0"
      }
    }
  }
}

And the hugepages value gets overwritten

bash-5.1# cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
0

hugepages settings generator exists of course

{
    ...
    "settings.kernel.sysctl.vm/nr_hugepages": "corndog generate-hugepages-setting",
    ...
}

3. Build a custom repo with 1.34.0 version that drops the setting generator. Upgrade the 1.33.0 node to the custom 1.34.0 version. Settings for the generated hugepages persists.

bash-5.1# apiclient get settings.kernel
{
  "settings": {
    "kernel": {
      "lockdown": "integrity",
      "sysctl": {
        "vm.nr_hugepages": "3000",
        "vm/nr_hugepages": "0"
      }
    }
  }
}

Settings generator for hugepages is removed, no entry ("vm/nr_hugepages") found in the setting generators.

3. Downgrade back to the 1.33.0 version. Settings generator for hugepages is showing up.

{
    ...
    "settings.kernel.sysctl.vm/nr_hugepages": "corndog generate-hugepages-setting",
    ...
}

Everything is exactly the same as observed from case 2.

5. On 1.33.0 version, manually set “vm/nr_hugepages” value to a non-zero value.

apiclient set --json '{"kernel": {"sysctl": {"vm/nr_hugepages": "3000"}}}'

Then upgrade to 1.34.0 again. Verified that the settings value persists while settings generator is removed (confirmed in case 3). This ensures customer who mitigated the issue by manually setting "vm/nr_hugepages" to the desired value will not be affected by the setting generator drop.

bash-5.1# apiclient get settings.kernel
{
  "settings": {
    "kernel": {
      "lockdown": "integrity",
      "sysctl": {
        "vm.nr_hugepages": "3000",
        "vm/nr_hugepages": "3000"
      }
    }
  }
}

bash-5.1# cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
3000

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.