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Title: POC: Memory profiler allocation labels by rudolf · Pull Request #62649 · nodejs/node · GitHub

Open Graph Title: POC: Memory profiler allocation labels by rudolf · Pull Request #62649 · nodejs/node

X Title: POC: Memory profiler allocation labels by rudolf · Pull Request #62649 · nodejs/node

Description: This is a POC for initial feedback. If we can get alignment within Node.js I could try to contribute the v8 changes upstream. Summary Adds the ability to tag sampling heap profiler allocations with string labels that propagate through async context (via CPED). This enables attributing memory usage to specific HTTP routes, tenants, or operations — something no JS runtime currently supports. V8 changes HeapProfileSampleLabelsCallback — embedder callback invoked on sampled allocations to retrieve labels from the current async context AllocationProfile::Sample::labels — key-value pairs on each sample (behind V8_HEAP_PROFILER_SAMPLE_LABELS compile flag) Datadog's Attila Szegedi proposed a similar label mechanism for CPU profiling on v8-dev (July 2025). V8 team (Leszek Swirski) indicated they would review non-invasive patches behind #ifdefs. This PR applies the same approach to heap profiling, which is simpler. Everything runs on the allocation thread with no signal-safety concerns. Node.js changes: v8.withHeapProfileLabels(labels, fn) — runs fn with labels that propagate across await v8.setHeapProfileLabels(labels) — sets labels for current async scope (for framework middleware patterns) v8.getAllocationProfile() returns samples[].labels and per-label externalBytes (Buffer/ArrayBuffer) ProfilingArrayBufferAllocator tracks external allocations per label (single atomic load overhead when disabled) #62273 landed the SyncHeapProfileHandle API with Symbol.dispose support. The labels API proposed here is complementary, it adds context (which route/tenant) to the samples that SyncHeapProfileHandle already collects. A follow-up could integrate withHeapProfileLabels as a method on the handle. Motivation In multi-tenant or multi-route Node.js servers, a memory spike today tells you how much memory grew but not what caused it. Operators resort to code inspection or heap snapshots but these don't scale to collecting data over long timespans for large deployments. With labeled heap/external memory profiling, you can answer "route /api/search accounts for 400MB of the 1.2GB heap" directly from production telemetry (e.g. via OTel). This mirrors Go's pprof.Labels capability Overhead 20-run benchmark (two-server realistic HTTP workload): Sampling profiler alone: 0.6% (not statistically significant) Sampling + labels: 2.2% total (p<0.01) When disabled: zero overhead (no code path changes) Test plan V8 cctests for label callback JS tests: label propagation across await, concurrent contexts, setHeapProfileLabels, external memory tracking, GC cleanup Micro and macro benchmarks in benchmark/v8/ and benchmark/http/

Open Graph Description: This is a POC for initial feedback. If we can get alignment within Node.js I could try to contribute the v8 changes upstream. Summary Adds the ability to tag sampling heap profiler allocations with...

X Description: This is a POC for initial feedback. If we can get alignment within Node.js I could try to contribute the v8 changes upstream. Summary Adds the ability to tag sampling heap profiler allocations with...

Opengraph URL: https://github.com/nodejs/node/pull/62649

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