Inconsistent Transparent Huge Pages (THP) settings across Photon OS Images in CNF deployments

Products

• VMware Telco Cloud Automation

Issue/Introduction

• Performance variances or deployment inconsistencies are observed across Cloud-Native Functions (CNFs) running on different Tanzu Kubernetes Grid (TKG) worker nodes.

• CNF pods requiring specific Transparent Huge Pages (THP) memory management settings exhibit unexpected behavior depending on the underlying base image version.

• To verify the active THP kernel argument set on the underlying worker nodes, run the following command on the target nodes:

  grep -o 'transparent_hugepage=[a-z]*' /proc/cmdline

 

Environment

TCA 3.4

Cause

• Default kernel boot parameters for Transparent Huge Pages vary across different build versions of Photon OS base images.
• When deploying worker nodes, this leads to configuration drift in kernel parameters, causing operational and performance discrepancies for CNFs that rely on standardized THP settings.

Resolution

To guarantee consistent THP kernel settings across all Photon OS versions during instantiation, explicitly specify the required GRUB kernel arguments within the CNF’s CSAR (Cloud Service Archive) descriptor file:

1. Open the CSAR node customization / blueprint configuration file.

2. Update the grub section under kernel_args to enforce the desired THP parameters:

grub:
  kernel_args:
    - "transparent_hugepage=always"
    # Optional: defrag mode adjustment
    - "transparent_hugepage_defrag=madvise"

3. Save and re-package the CSAR.

4. Onboard the updated CSAR to the VMware Telco Cloud Automation (TCA) catalog and proceed with CNF instantiation.

Additional Information

• Explicitly passing kernel parameters via the CSAR ensures that VMware TCA and the NodeConfig operator override base image defaults at runtime.
• This guarantees uniform THP configurations across all nodes regardless of the underlying Photon OS image version.

Note: If you run different Photon versions in the environment, then run a command grep -o 'transparent_hugepage=[a-z]*' /proc/cmdline before applying CSAR settings. If the output differs then apply the CSAR or you no need to push this settings.