Fix native OOM from unbounded CallTraceHashTable expansion by jbachorik · Pull Request #670 · DataDog/java-profiler

jbachorik · 2026-07-17T18:25:43Z

Problem

Under live-heap profiling (memory=...:l) with a long-running, unrotated recording, the profiler can exhaust native address space and crash with os::commit_memory ... failed; error='Not enough space' (errno=12) / pthread_create failed (EAGAIN). The failure is vm.max_map_count (VMA) exhaustion, not RAM: a captured memory map showed tens of thousands of 8 MB (and 8 MB-multiple) anonymous regions.

Root cause

CallTraceHashTable grows its backing LongHashTable by doubling capacity, allocating each generation from a LinearAllocator whose chunks are a fixed 8 MB (CALL_TRACE_CHUNK). Once a table's byte size exceeds one chunk (capacity ≥ ~512K entries), LinearAllocator::alloc() can never place it: the bump-allocator's inner loop only fits offs + size <= _chunk_size, so an oversized request falls through to getNextChunk(), which allocates a fresh 8 MB chunk that also can't fit it — looping and allocating chunks until mmap fails.

The active table only grows this large between processTraces() rotations (which reset it to the initial capacity). In a single start-to-end JFR recording no rotation happens, so under the high distinct-trace volume that live-heap sampling sustains, the table crosses the one-chunk threshold and the allocator runs away.

Fix

expandTableIfNeeded() now refuses to expand when the next generation's getSize() would exceed LinearAllocator::maxAllocatableSize() (one chunk minus its header). Instead of an unbounded allocation loop, put() keeps working on the current table at a higher load factor; the next rotation resets it. The bound is derived from the chunk size, so it stays correct if CALL_TRACE_CHUNK changes. A new calltrace_storage_expansion_skipped counter records when the cap engages.

This also includes a related per-thread native leak fix in LivenessTracker: its subsampling RNG ThreadLocals (gen/dis/skipped) were reclaimed only via pthread-key destructors, which never fire when a JNI-attached thread detaches on a reused OS thread. They are now released explicitly from Profiler::onThreadEnd(), matching how the CPU/wall engines and ProfiledThread are already torn down.

Validation

Reproducer (renaissance akka-uct -r 20 under memory=64:l) OOM'd at ~90 s / 13 iterations before the fix. With the fix it completes all 20 iterations with peak VMA count in the hundreds (was pinned at the 65530 limit). Compiles clean; verified the change is compatible with the existing expandTableIfNeeded/overflow-guard unit tests by inspection (the new check sits alongside the existing guards and only engages for tables that exceed one chunk).

🤖 Generated with Claude Code

dd-octo-sts · 2026-07-17T18:56:45Z

Benchmark Results (commit `75285e9`)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/125374352 Commit: 75285e92c193b1b4eedd58201cecc5e0f6694060

✅ Within expected boundaries

No significant runtime deltas (all within run-to-run noise) and no internal-counter outliers.

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10181 ms (21 iters)	✅ 10290 ms (21 iters)	≈ +1.1% (±10.8%)	— / —
finagle-chirper	21	✅ 5949 ms (33 iters)	✅ 5906 ms (33 iters)	≈ -0.7% (±25.3%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5510 ms (36 iters)	✅ 5495 ms (36 iters)	≈ -0.3% (±25.2%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2716 ms (69 iters)	✅ 2726 ms (68 iters)	≈ +0.4% (±2.7%)	— / —
fj-kmeans	25	✅ 2866 ms (66 iters)	✅ 2832 ms (66 iters)	≈ -1.2% (±2.5%)	— / —
future-genetic	21	✅ 2037 ms (90 iters)	✅ 2073 ms (90 iters)	≈ +1.8% (±2.6%)	— / —
future-genetic	25	✅ 2063 ms (90 iters)	✅ 2048 ms (90 iters)	≈ -0.7% (±2.9%)	— / —
naive-bayes	21	✅ 1299 ms (132 iters)	✅ 1277 ms (134 iters)	≈ -1.7% (±32.4%)	— / —
naive-bayes	25	✅ 1018 ms (168 iters)	✅ 1004 ms (170 iters)	≈ -1.4% (±31.4%)	— / —
reactors	21	✅ 16455 ms (15 iters)	✅ 16332 ms (15 iters)	≈ -0.7% (±8.1%)	— / —
reactors	25	✅ 18441 ms (15 iters)	✅ 18882 ms (15 iters)	≈ +2.4% (±4.1%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	1 / 2	1952 / 1942	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	1 / 3	2169 / 2356	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	4 / 2	8479 / 8210	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	✅ / ✅	8416 / 8155	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	1 / 5	1282 / 1277	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	3 / 3	1298 / 1255	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	2 / 2	2922 / 2931	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	2 / 1	2888 / 2859	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	4 / 4	3531 / 3536	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	3 / 4	3463 / 3494	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	✅ / ✅	1612 / 1596	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	✅ / 1	1952 / 1935	✅ / ✅	✅ / ✅

zhengyu123 · 2026-07-20T13:27:39Z

Could you rebase the PR? seems it has conflicts.

CallTraceHashTable grows its backing LongHashTable by doubling capacity from a LinearAllocator whose chunks are a fixed 8MB. Once a table exceeds one chunk (capacity >= 512K entries), LinearAllocator::alloc() can never place it: the bump-allocator loops allocating fresh chunks that still cannot fit the oversized request, until mmap fails - a native OOM / vm.max_map_count exhaustion, not a heap-space error. This is reachable under live-heap profiling (memory=...:l) with a long, unrotated recording, where the active table grows past that threshold between processTraces() rotations. Cap expansion at the largest table that fits in one allocator chunk (LinearAllocator::maxAllocatableSize()); further growth degrades put() to a higher load factor and recovers on the next rotation. Deriving the bound from the chunk size keeps it correct if the chunk size ever changes. Also fix a per-thread native leak in LivenessTracker's subsampling RNG state: the gen/dis/skipped ThreadLocals were reclaimed only via pthread-key destructors, which never fire when a JNI-attached thread detaches on a reused OS thread. Release them explicitly from Profiler::onThreadEnd(), matching how the CPU/wall engines and ProfiledThread are already torn down. Environment: Datadog workspace Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

dd-octo-sts · 2026-07-20T13:59:29Z

CI Test Results

Run:#29814088134 | Commit:a81a45d | Duration: 15m 58s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
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: 32 | Passed: 32 | Failed: 0

Updated: 2026-07-21 09:05:25 UTC

…abot Dependabot bumped analyze to v4.37.1 without init, causing CodeQL's "Loaded a configuration file for version X, but running version Y" error.

dd-octo-sts · 2026-07-20T15:27:54Z

Benchmark Results (commit `d1d5076`)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/125698320 Commit: d1d5076612a3fda65dd1f7d127e02b995b55fc59

⚠️ Significant outliers

🔴 fj-kmeans (JDK 21): runtime +6.1% (2663→2825 ms)
🔴 future-genetic (JDK 25): runtime +5% (2022→2124 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10276 ms (21 iters)	✅ 10386 ms (21 iters)	≈ +1.1% (±10.9%)	— / —
akka-uct	25	✅ 8869 ms (24 iters)	✅ 8909 ms (24 iters)	≈ +0.5% (±10.4%)	— / —
finagle-chirper	21	✅ 5960 ms (33 iters)	✅ 5984 ms (33 iters)	≈ +0.4% (±25.1%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5462 ms (36 iters)	✅ 5542 ms (36 iters)	≈ +1.5% (±24.9%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2663 ms (70 iters)	✅ 2825 ms (66 iters)	🔴 +6.1%	— / —
fj-kmeans	25	✅ 2834 ms (66 iters)	✅ 2818 ms (66 iters)	≈ -0.6% (±2.6%)	— / —
future-genetic	21	✅ 2058 ms (90 iters)	✅ 2044 ms (90 iters)	≈ -0.7% (±2.5%)	— / —
future-genetic	25	✅ 2022 ms (91 iters)	✅ 2124 ms (87 iters)	🔴 +5%	— / —
naive-bayes	21	✅ 1233 ms (138 iters)	✅ 1245 ms (137 iters)	≈ +1% (±33.1%)	— / —
naive-bayes	25	✅ 1009 ms (169 iters)	✅ 1010 ms (169 iters)	≈ +0.1% (±31.5%)	— / —
reactors	21	✅ 16270 ms (15 iters)	✅ 15718 ms (15 iters)	≈ -3.4% (±6%)	— / —
reactors	25	✅ 19058 ms (15 iters)	✅ 18294 ms (15 iters)	≈ -4% (±4.9%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	2 / 3	2042 / 1952	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	2 / 4	2251 / 2204	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	4 / 3	8718 / 8771	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	✅ / 2	8527 / 8342	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	✅ / ✅	✅ / ✅	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	1 / 4	1270 / 1292	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	2 / 1	3042 / 2917	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	✅ / ✅	2833 / 2919	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	7 / 7	3462 / 3491	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	4 / 3	3463 / 3490	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	1 / ✅	1696 / 1521	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	2 / ✅	1978 / 1919	✅ / ✅	✅ / ✅

dd-octo-sts · 2026-07-20T15:30:21Z

Reliability & Chaos Results

✅ All reliability & chaos checks passed Pipeline: https://gitlab.ddbuild.io/DataDog/java-profiler/-/pipelines/125698277

zhengyu123

LGTM

kaahos

apart from the missing copyrights, it looks good to me!

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datadog-datadog-prod-us1 · 2026-07-21T08:51:18Z

Tests

🔄 Datadog auto-retried 2 jobs - 2 passed on retry

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: b159f4e | Docs | Datadog PR Page | Give us feedback!}

dd-octo-sts · 2026-07-21T08:53:59Z

Benchmark Results (commit `b159f4e`)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/125887870 Commit: b159f4e0e4a132c2d43e443f179f44663931cb94

⚠️ Significant outliers

🟢 future-genetic (JDK 25): runtime -3.2% (2074→2008 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10319 ms (21 iters)	✅ 10341 ms (21 iters)	≈ +0.2% (±11.1%)	— / —
akka-uct	25	✅ 8856 ms (24 iters)	✅ 8805 ms (24 iters)	≈ -0.6% (±10.3%)	— / —
finagle-chirper	21	✅ 5940 ms (33 iters)	✅ 5938 ms (33 iters)	≈ -0% (±25.7%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5533 ms (35 iters)	✅ 5496 ms (36 iters)	≈ -0.7% (±24.5%)	⚠️ W:3 / ⚠️ W:4
fj-kmeans	21	✅ 2784 ms (67 iters)	✅ 2770 ms (67 iters)	≈ -0.5% (±2.7%)	— / —
fj-kmeans	25	✅ 2774 ms (67 iters)	✅ 2819 ms (66 iters)	≈ +1.6% (±2.7%)	— / —
future-genetic	21	✅ 2095 ms (88 iters)	✅ 2112 ms (87 iters)	≈ +0.8% (±2.9%)	— / —
future-genetic	25	✅ 2074 ms (90 iters)	✅ 2008 ms (93 iters)	🟢 -3.2%	— / —
naive-bayes	21	✅ 1267 ms (135 iters)	✅ 1231 ms (139 iters)	≈ -2.8% (±32.3%)	— / —
naive-bayes	25	✅ 1010 ms (169 iters)	✅ 1015 ms (168 iters)	≈ +0.5% (±31.7%)	— / —
reactors	21	✅ 15746 ms (15 iters)	✅ 16228 ms (15 iters)	≈ +3.1% (±6.1%)	— / —
reactors	25	✅ 17941 ms (15 iters)	✅ 18765 ms (15 iters)	≈ +4.6% (±5.6%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	1 / ✅	1925 / 2009	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	2 / 3	2253 / 2239	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	2 / 2	8371 / 8786	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	2 / 2	8047 / 8448	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	1 / 4	1252 / 1245	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	4 / ✅	1284 / 1261	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	1 / ✅	2935 / 2848	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	3 / 1	2984 / 2948	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	3 / 6	3512 / 3484	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	5 / 4	3469 / 3505	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	4 / 1	1562 / 1503	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	2 / ✅	1806 / 1940	✅ / ✅	✅ / ✅

jbachorik requested a review from a team as a code owner July 17, 2026 18:25

jbachorik force-pushed the jb/fix-liveheap-calltrace-oom branch from 75285e9 to c9d17a9Compare July 20, 2026 13:38

Fix codeql-action init/analyze version mismatch, group them in depend…
d1d5076
…abot Dependabot bumped analyze to v4.37.1 without init, causing CodeQL's "Loaded a configuration file for version X, but running version Y" error.

zhengyu123 approved these changes Jul 20, 2026
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kaahos approved these changes Jul 20, 2026
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Comment threadddprof-lib/src/main/cpp/livenessTracker.h Outdated
Comment threadddprof-lib/src/main/cpp/callTraceHashTable.cpp Outdated

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b159f4e

CopilotAI review requested due to automatic review settings July 21, 2026 08:23

CopilotAI reviewed Jul 21, 2026

jbachorik merged commit 77c2122 into mainJul 21, 2026
180 of 182 checks passed

jbachorik deleted the jb/fix-liveheap-calltrace-oom branch July 21, 2026 09:11

github-actionsBot added this to the 1.47.0 milestone Jul 21, 2026

rkennke mentioned this pull request Jul 23, 2026
Bump java-profiler (ddprof) to 1.47.0 DataDog/dd-trace-java#12055
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Fix native OOM from unbounded CallTraceHashTable expansion - #670

Fix native OOM from unbounded CallTraceHashTable expansion#670
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jbachorik commented Jul 17, 2026

Problem

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Fix

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Benchmark Results (commit 75285e9)

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Benchmark Results (commit d1d5076)

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Reliability & Chaos Results

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