memory: apply cgroup limit immediately

[okJiang]

What problem does this PR solve?

Issue Number: ref #10719

When PD is started by systemd under a cgroup, package initialization can cache the host physical memory before InitMemoryHook selects the cgroup memory hooks.

Because the total-memory cache remains valid for 60 seconds, RegionSyncer can size its history buffer using the host memory and retain an oversized limit for the process lifetime.

What is changed and how does it work?

When InitMemoryHook selects cgroup memory hooks, immediately replace the cached total memory with the detected cgroup limit and invalidate the cached memory usage.

Add a regression test that verifies stale physical-memory cache entries are replaced during the hook switch.

Check List

Tests

• Unit test
• Manual test

Manual test:

• Verified PD startup with 2, 4, 8, 16, and 32 GiB cgroup limits.
• Verified the corresponding RegionSync history capacities were 10k, 10k, 20k, 40k, and 80k.

Release note

Fix PD memory-aware sizing to use the cgroup memory limit immediately at startup.

Summary by CodeRabbit

• Bug Fixes

  • Improved memory reporting in cgroup environments by using the detected cgroup memory limit and current usage.
  • Ensured cached memory values refresh correctly when cgroup-based limits are applied.

• Tests

  • Added coverage to verify accurate memory totals and cache invalidation when switching to cgroup memory data.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 2410d9d8-1843-4fe9-8abb-988a8531338a

📥 Commits

Reviewing files that changed from the base of the PR and between fad3ff9 and 550a135.

📒 Files selected for processing (2)

• pkg/memory/meminfo.go
• pkg/memory/meminfo_test.go

---

📝 Walkthrough

Walkthrough

InitMemoryHook now uses a helper to switch to cgroup memory readers and refresh cached limits and usage. A new test verifies the cgroup total and invalidated usage cache.

Changes

Cgroup memory hook

Layer / File(s)	Summary
Cgroup hook and cache update pkg/memory/meminfo.go	The cgroup branch calls useCgroupMemoryHook, which selects cgroup readers, updates memLimit, and invalidates memUsage.
Hook cache test coverage pkg/memory/meminfo_test.go	Adds leak-checking test setup and verifies the cgroup total and reset usage timestamp while restoring shared state.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main change: applying the cgroup memory limit immediately.
Description check	✅ Passed	The description matches the template with problem, change details, tests, manual validation, and a release note.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

@okJiang: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-unit-test-next-gen-3	550a135	link	true	/test pull-unit-test-next-gen-3

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[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.32%. Comparing base (070828c) to head (550a135).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11063      +/-   ##
==========================================
+ Coverage   79.23%   79.32%   +0.09%     
==========================================
  Files         540      541       +1     
  Lines       76010    76358     +348     
==========================================
+ Hits        60226    60571     +345     
- Misses      11533    11535       +2     
- Partials     4251     4252       +1     

Flag	Coverage Δ
unittests	79.32% <83.33%> (+0.09%)	⬆️

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