[kaahos]

What does this PR do?:

Correct the small-allocation overhead expectation and add separate regression coverage for successful and inconclusive header discovery. Check footprint and accounting totals against allocator-reported usable sizes after allocations and partial frees.

Motivation:

The ARM64 release job in #877 reports a zero header estimate and 104 usable bytes for a 96-byte request. That is 8.33% observed overhead, which fails the existing assertion that requires more than 10%. Zero is an explicit fallback when the header probe is inconclusive.

Accepting that fallback also needs a separate test that requires a nonzero estimate when contiguous allocations expose a header. Otherwise an estimator that always returns zero could pass unnoticed.

Additional Notes:

• Production code is unchanged.
• Retain the 2,000-node map scenario. Observe actual rebound node allocations and check exact logical-byte and overhead totals after inserts, partial erases, and container destruction. Expected overhead uses allocator-reported usable sizes plus the cached header estimate.
• A standalone executable prepares contiguous and fragmented layouts using real glibc allocations before the first cached header probe. Both layouts execute the same percentage assertions as the main test. Its layout preconditions fail explicitly if they are not met.
• The isolated probe checks run on glibc. The main accounting checks retain the active platform or sanitizer allocator.
• Independent agentic review: passed, no remaining findings.

How to test the change?:

Passed on Linux ARM64:

./.claude/commands/build-and-summarize spotlessApply :ddprof-lib:gtestDebug_mallocFootprint_ut :ddprof-lib:gtestRelease_mallocFootprint_ut :ddprof-lib:gtestDebug_countingAllocator_ut
./.claude/commands/build-and-summarize :ddprof-lib:gtestAsan_mallocFootprint_ut -Pnative.forceCompiler=g++

• Debug and release: all 7 footprint tests pass under both normal startup and reproduced zero-header startup.
• Both isolated allocator layouts also pass on Linux x64.
• A map-node-only overhead mutation passes the direct-allocation test and fails the map scenario, confirming distinct coverage.
• Temporary mutation checks reject the original small_pct > 10 assertion, an always-zero header estimate, omitted usable-size rounding, and omitted CountingAllocator overhead recording.

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a security review (run the dd:platform-security-review
  skill, or file a request via the PSEC review form).
  bewaire also runs automatically on every PR.
• This PR doesn't touch any of that.
• JIRA: N/A; regression observed in fix(profiler): mark skipped frozen virtual-thread callers as truncated #877.

Unsure? Have a question? Request a review!

[dd-octo-sts]

CI Test Results

Run: #41047605373 | Commit: 4611617 | Duration: 20m 9s (longest job)

✅ All 108 test jobs passed

Status Overview

JDK	glibc-aarch64/asan	glibc-aarch64/debug	glibc-aarch64/release	glibc-aarch64/tsan	glibc-amd64/asan	glibc-amd64/debug	glibc-amd64/release	glibc-amd64/tsan	musl-aarch64/debug	musl-aarch64/release	musl-amd64/debug	musl-amd64/release
8	-	-	-	-	✅	✅	✅	✅	-	-	-	-
8-ibm	-	-	-	-	✅	✅	✅	✅	-	-	-	-
8-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
8-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
8-orcl	-	-	-	-	✅	✅	✅	✅	-	-	-	-
11	-	-	-	-	✅	✅	✅	✅	-	-	-	-
11-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
11-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
17	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-j9	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
17-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
21	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
21-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
21-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅
25	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
25-graal	✅	✅	✅	✅	✅	✅	✅	✅	-	-	-	-
25-librca	-	-	-	-	-	-	-	-	✅	✅	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 108 | Passed: 108 | Failed: 0

---

Updated: 2026-10-30 11:44:59 UTC

[dd-octo-sts]

✅ All 40 integration tests passed

📊 Dashboard · 👷 Pipeline · 📦 00578a23

[kaahos]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-27T14:29:41.312215Z	c86fe0d	Manual request

ℹ️ About Codex in GitHub

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• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c86fe0d69c

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[jbachorik]

💡 Sphinx Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c86fe0d

[jbachorik]

🔵 Sphinx review — INFO

Finding — Mutation test-adequacy analysis skipped 334 test-path candidates in: ddprof-lib/src/test/cpp/mallocFootprintChecks.h, ddprof-lib/src/test/cpp/mallocFootprint_ut.cpp, ddprof-lib/src/test/resources/native-libs/malloc-footprint-probe/Makefile, ddprof-lib/src/test/resources/native-libs/malloc-footprint-probe/main.cpp. These test files were not assessed; verify they actually pin the change under review.

Suggestion — Confirm the added or changed tests cover the modified behavior, or note the gap explicitly.

[dd-octo-sts]

Reliability & Chaos Results

✅ All reliability & chaos checks passed Pipeline: https://gitlab.ddbuild.io/DataDog/java-profiler/-/pipelines/148886730