Implementing Policy Groups for Enhanced Memory Management in Linux

Introduction

Memory management in Linux has long relied on the kernel's control-group (cgroups) subsystem, which works well for resource management, as Chris Li noted during the memory-management track at the 2026 Linux Storage, Filesystem, Memory Management, and BPF Summit. However, cgroups falls short for other use cases, particularly where flexible policy-based grouping is needed. Li proposed an enhancement called policy groups to address these shortcomings, though a consensus on the feature's final shape remains elusive. This guide walks you through understanding and evaluating policy groups, and how you might implement them for improved memory management in your Linux system.

What You Need

• A Linux system (preferably with a recent kernel version) for testing
• Access to kernel source code and build tools (e.g., gcc, make)
• Familiarity with existing cgroup subsystems and memory management concepts
• Patience and preparedness to work with experimental kernel features
• A dedicated test environment (virtual machine or isolated partition)

Step-by-Step Guide

1. Assess Current cgroups Limitations

   Start by reviewing how you currently use cgroups for memory management. Identify specific pain points such as rigid hierarchical policies, difficulty in applying per-application memory limits without affecting other tasks, or overhead from frequent policy changes. Document these issues—they'll guide your evaluation of policy groups.

2. Understand the Policy Groups Proposal

   Chris Li's policy groups extend the idea of grouping tasks based on policy rather than resource quotas. Unlike cgroups, which tie resource controls directly to the group, policy groups separate policy definitions from resource enforcement. Read up on the proposal (available from kernel mailing list archives or LWN.net) to grasp the core concepts: policy groups can override or supplement cgroups, allowing more granular memory management for diverse workloads.

3. Prepare Your Environment

   Since policy groups are not yet merged into mainline, you'll need to apply the proposed patches. Obtain the patch set from the latest Linux kernel mailing list submissions (mm or linux-kernel). Apply the patches to your kernel source and build a custom kernel. Ensure you enable CONFIG_CGROUP_POLICY in your kernel configuration. Boot into this kernel on your test system.

4. Define Policy Groups for Memory Management

   With the patched kernel, you can now create policy groups via the new /sys/fs/cgroup/policy/ filesystem. Start simple: create a policy group and assign a few processes to it. Use a text editor or scripts to set memory policies such as soft limits, throttling rules, or allocation preferences. For example, you might set a low-priority policy for background tasks while giving foreground apps higher memory priority.

5. Integrate with Existing cgroups Hierarchies

   Policy groups can work alongside traditional cgroups. Map your new policy groups onto existing cgroups to see how they interact. For instance, you can assign a policy group to a cgroup's tasks without changing the original resource limits. Monitor memory usage and system behavior using tools like htop or perf to verify that policies are being respected.

6. Test and Iterate

   Design test scenarios that expose the shortcomings you identified in Step 1. Run workloads that previously caused issues—e.g., multiple memory-intensive applications with conflicting demands. Iterate on your policy definitions: adjust priorities, set conditional rules, and observe changes in memory pressure and swapping. Record results for community feedback.

7. Engage with the Community

   Share your findings on the Linux kernel mailing list, particularly in threads about policy groups. Provide detailed reports of what worked and what didn't, along with performance data. Your real-world testing can help shape the final design—especially since consensus is still distant. Follow the discussion and contribute suggestions.

Tips

• Stay updated: Policy groups are a moving target. Subscribe to LWN and the linux-mm list for the latest developments.
• Work incrementally: Start with one policy group and expand gradually. Overcomplicating early on can lead to confusion.
• Document your policies: Use clear naming and annotation so you can revert or share configurations easily.
• Respect kernel stability: Policy groups are experimental; never rely on them in production without extensive testing.
• Collaborate: If you encounter bugs or limitations, report them constructively to help the community reach a consensus faster.