[Metricbeat] Add memory PSI metrics for cgroupv2

[orestisfl]

Proposed commit message

Add memory pressure PSI metrics to the system.process.cgroup.memory
metricset, complementing the existing CPU and IO pressure metrics.

New fields added under system.process.cgroup.memory.pressure:

• pressure.some.{10,60,300}.pct - Share of time with some tasks stalled
• pressure.some.total - Total some pressure time
• pressure.full.{10,60,300}.pct - Share of time with all tasks stalled
• pressure.full.total - Total full pressure time

Closes #47604

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

How to test this PR locally

1. Build and Run Metricbeat

cd metricbeat
go build .

2. Create Test Configuration

metricbeat.modules:
- module: system
  period: 5s
  metricsets:
    - process
  processes: ['.*']
  process.cgroups.enabled: true

output.console:
  pretty: true

3. Run Metricbeat

./metricbeat -e -c /tmp/metricbeat-psi-test.yml

4. Verify Memory Pressure Fields

Look for system.process.cgroup.memory.pressure in the output:

"memory": {
  "pressure": {
    "some": {
      "10": { "pct": 0 },
      "60": { "pct": 0 },
      "300": { "pct": 0 },
      "total": 0
    },
    "full": {
      "10": { "pct": 0 },
      "60": { "pct": 0 },
      "300": { "pct": 0 },
      "total": 0
    }
  }
}

5. Compare Before/After (Optional)

compare-psi-metrics.sh
Use the comparison script to compare output from main vs this PR:

compare-psi-metrics.sh
Usage: ./compare-psi-metrics.sh <main-output.ndjson> <pr-output.ndjson>

Related issues

• Requires [cgv2] Add memory PSI metrics elastic-agent-system-metrics#274
• Closes [Metricbeat][System module] Report memory pressure stall information in metrics (Linux) #47604

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @orestisfl? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[github-actions]

🔍 Preview links for changed docs

• docs/reference/metricbeat/exported-fields-system.md
• docs/reference/metricbeat/metricbeat-metricset-system-process.md

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[colleenmcginnis]

Starting with v9.0, there is no longer a new documentation set published with every minor release: the same page stays valid over time and shows version-related evolutions (ref). As a result, we add version information in the fields.yml and it adds version badges to the generated Markdown file. Read more in Contributing to the docs.

Based on the backport labels, I assumed these changes are targeting 9.3.0, but feel free to adjust as needed. After applying the suggestions you'll have to regenerate the docs.

[colleenmcginnis]

You'll have to regenerate the docs (make update) to get the check-docs check to pass.

[colleenmcginnis]

✨