feat(scripts): Bun.gc relief evaluation harness (SIGUSR2 GC channel, matched arms)

devlog/_plan/260822_260822-bun14-followup-memory/020_watchdog_gc_relief.md

@@ -99,3 +99,41 @@ attached — goalplan c3 satisfied by construction.
 
 
 
+
+## Phase A verdict (2026-08-22): FAIL — Phase B not implemented
+
+Real runs (smoke:false), 3 fresh-process runs per arm per cell type, Bun 1.4.0
+darwin/arm64 on BOTH hosts (local dev Mac + macmini-cf). Evidence:
+evidence/gc-eval-local-darwin-arm64.json, evidence/gc-eval-macmini-darwin-arm64.json.
+
+### Criterion (a): ≥50% of post-load RSS growth gone by +60s after one GC
+
+| host | arm | rssAfterLoad (3 runs) | recoveredByPlus60s (3 runs) |
+|---|---|---|---|
+| macmini-cf | control | 305.0 / 302.2 / 354.8 MB | +0.25 / +0.23 / +0.26 MB |
+| macmini-cf | gc | 330.6 / 316.4 / 311.1 MB | −0.03 / +0.13 / +0.15 MB |
+| local | control | 329.1 / 304.1 / 325.9 MB | +0.21 / +0.23 / +0.23 MB |
+| local | gc | 332.5 / 324.1 / 334.1 MB | +0.13 / +0.11 / +0.10 MB |
+
+GC recovery is indistinguishable from control idle drift (<0.1% of load-height
+RSS on every run; the GC arm recovered LESS than control on 4 of 6 runs).
+Bun 1.4's shared-allocator Bun.gc(true) does NOT return the post-load RSS
+plateau on darwin — same qualitative result as the 1.3.x finding that produced
+the 260731 gate. Criterion (a) FAIL, decisively, on both hosts.
+
+### Criterion (c): latency (informational, gate already failed)
+
+GC pause (child-reported): 3.9–4.6 ms across all runs. Probe p99 deltas within
+noise (macmini 79.6→81.1/78.3/79.2 ms; local one outlier 84.1 vs 69.8 ms
+control). No acceptance computed — (a) already fails the gate.
+
+### Consequence
+
+- The 260731 ban on production threshold/idle Bun.gc(true) STANDS on Bun 1.4.
+- Phase B (config-gated watchdog relief, idle gate, lastReliefAt, wiring chain)
+  is NOT implemented. The design remains in this doc for a future Bun release
+  that changes allocator page-return behavior; re-run this harness first.
+- The RSS plateau after SSE load is allocator page retention, not JS-heap
+  garbage — consistent with the 260731 analysis; process recycling remains the
+  operational lever.
+

devlog/_plan/260822_260822-bun14-followup-memory/evidence/gc-eval-local-darwin-arm64.json

@@ -0,0 +1,152 @@
+{
+  "smoke": false,
+  "bunVersion": "1.4.0",
+  "bunRevision": "34cbb9a40b4bd1bd767d134a7065e66c2432a676",
+  "platform": "darwin",
+  "arch": "arm64",
+  "at": "2026-08-21T16:02:16.941Z",
+  "runs": 3,
+  "loadTurns": 30,
+  "events": 200,
+  "eventBytes": 65536,
+  "results": [
+    {
+      "kind": "rss",
+      "arm": "control",
+      "runIndex": 0,
+      "smoke": false,
+      "rssAfterLoad": 329072640,
+      "rssPlus5s": 329121792,
+      "rssPlus60s": 328859648,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 212992
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 0,
+      "smoke": false,
+      "rssAfterLoad": 332513280,
+      "rssPlus5s": 332660736,
+      "rssPlus60s": 332382208,
+      "gcDurationMs": 4.322166,
+      "recoveredByPlus60s": 131072
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 0,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 66.84818750000704,
+      "p99Ms": 69.78122875000263,
+      "maxMs": 69.89625000000524,
+      "gcDurationMs": null,
+      "rssNonNormative": 358809600
+    },
+    {
+      "kind": "latency",
+      "arm": "gc",
+      "runIndex": 0,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 66.28095900000335,
+      "p99Ms": 69.86663276999433,
+      "maxMs": 70.19816699999501,
+      "gcDurationMs": 4.599541,
+      "rssNonNormative": 333365248
+    },
+    {
+      "kind": "rss",
+      "arm": "control",
+      "runIndex": 1,
+      "smoke": false,
+      "rssAfterLoad": 304119808,
+      "rssPlus5s": 304185344,
+      "rssPlus60s": 303890432,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 229376
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 1,
+      "smoke": false,
+      "rssAfterLoad": 324059136,
+      "rssPlus5s": 324190208,
+      "rssPlus60s": 323944448,
+      "gcDurationMs": 4.1755,
+      "recoveredByPlus60s": 114688
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 1,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 66.12091649998911,
+      "p99Ms": 70.72656152000272,
+      "maxMs": 71.06291700000293,
+      "gcDurationMs": null,
+      "rssNonNormative": 366297088
+    },
+    {
+      "kind": "latency",
+      "arm": "gc",
+      "runIndex": 1,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 66.67666649997409,
+      "p99Ms": 68.93200429000456,
+      "maxMs": 68.9802090000012,
+      "gcDurationMs": 4.379583,
+      "rssNonNormative": 360906752
+    },
+    {
+      "kind": "rss",
+      "arm": "control",
+      "runIndex": 2,
+      "smoke": false,
+      "rssAfterLoad": 325877760,
+      "rssPlus5s": 325926912,
+      "rssPlus60s": 325648384,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 229376
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 2,
+      "smoke": false,
+      "rssAfterLoad": 334053376,
+      "rssPlus5s": 334233600,
+      "rssPlus60s": 333955072,
+      "gcDurationMs": 4.560834,
+      "recoveredByPlus60s": 98304
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 2,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 67.00995850001345,
+      "p99Ms": 71.89010472996858,
+      "maxMs": 72.32308299996657,
+      "gcDurationMs": null,
+      "rssNonNormative": 347078656
+    },
+    {
+      "kind": "latency",
+      "arm": "gc",
+      "runIndex": 2,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 66.42141650000121,
+      "p99Ms": 84.07492050000349,
+      "maxMs": 85.31870800000615,
+      "gcDurationMs": 4.345833,
+      "rssNonNormative": 319455232
+    }
+  ]
+}

devlog/_plan/260822_260822-bun14-followup-memory/evidence/gc-eval-macmini-darwin-arm64.json

@@ -0,0 +1,152 @@
+{
+  "smoke": false,
+  "bunVersion": "1.4.0",
+  "bunRevision": "34cbb9a40b4bd1bd767d134a7065e66c2432a676",
+  "platform": "darwin",
+  "arch": "arm64",
+  "at": "2026-08-21T16:02:06.458Z",
+  "runs": 3,
+  "loadTurns": 30,
+  "events": 200,
+  "eventBytes": 65536,
+  "results": [
+    {
+      "kind": "rss",
+      "arm": "control",
+      "runIndex": 0,
+      "smoke": false,
+      "rssAfterLoad": 305037312,
+      "rssPlus5s": 305086464,
+      "rssPlus60s": 304791552,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 245760
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 0,
+      "smoke": false,
+      "rssAfterLoad": 330563584,
+      "rssPlus5s": 330711040,
+      "rssPlus60s": 330596352,
+      "gcDurationMs": 4.067541,
+      "recoveredByPlus60s": -32768
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 0,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 75.82177049999154,
+      "p99Ms": 79.6427512700003,
+      "maxMs": 79.90070800000103,
+      "gcDurationMs": null,
+      "rssNonNormative": 354353152
+    },
+    {
+      "kind": "latency",
+      "arm": "gc",
+      "runIndex": 0,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 76.33122900000308,
+      "p99Ms": 81.13658803999365,
+      "maxMs": 81.63145899999654,
+      "gcDurationMs": 4.23,
+      "rssNonNormative": 330596352
+    },
+    {
+      "kind": "rss",
+      "arm": "control",
+      "runIndex": 1,
+      "smoke": false,
+      "rssAfterLoad": 302235648,
+      "rssPlus5s": 302301184,
+      "rssPlus60s": 302006272,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 229376
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 1,
+      "smoke": false,
+      "rssAfterLoad": 316375040,
+      "rssPlus5s": 316522496,
+      "rssPlus60s": 316243968,
+      "gcDurationMs": 4.252875,
+      "recoveredByPlus60s": 131072
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 1,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 76.29347899998538,
+      "p99Ms": 79.48590976999724,
+      "maxMs": 79.50983399999677,
+      "gcDurationMs": null,
+      "rssNonNormative": 324976640
+    },
+    {
+      "kind": "latency",
+      "arm": "gc",
+      "runIndex": 1,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 75.3432090000133,
+      "p99Ms": 78.32939928999403,
+      "maxMs": 78.33808399998816,
+      "gcDurationMs": 4.057542,
+      "rssNonNormative": 334856192
+    },
+    {
+      "kind": "rss",
+      "arm": "control",
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+      "smoke": false,
+      "rssAfterLoad": 354811904,
+      "rssPlus5s": 354877440,
+      "rssPlus60s": 354549760,
+      "gcDurationMs": null,
+      "recoveredByPlus60s": 262144
+    },
+    {
+      "kind": "rss",
+      "arm": "gc",
+      "runIndex": 2,
+      "smoke": false,
+      "rssAfterLoad": 311148544,
+      "rssPlus5s": 311279616,
+      "rssPlus60s": 311001088,
+      "gcDurationMs": 3.892,
+      "recoveredByPlus60s": 147456
+    },
+    {
+      "kind": "latency",
+      "arm": "control",
+      "runIndex": 2,
+      "smoke": false,
+      "probeTurns": 20,
+      "p50Ms": 75.67283349999343,
+      "p99Ms": 79.54803673004673,
+      "maxMs": 79.55712500005029,
+      "gcDurationMs": null,
+      "rssNonNormative": 342310912
+    },
+    {
+      "kind": "latency",
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+      "smoke": false,
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+      "p99Ms": 79.18780874996737,
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+      "gcDurationMs": 3.921584,
+      "rssNonNormative": 375390208
+    }
+  ]
+}