russell@unturf.com
3f1b1bc0ab
Adds §6.6.3 "Collaborative Meta-GC: From Greedy to Adaptive" with
the three-workload benchmark (friendly / hostile / mixed × greedy
/ adaptive). Honest read of the numbers:
friendly greedy 732 ms 1000 resets, 0 escapes
friendly adaptive 691 ms 1000 resets, 0 escapes (-6%)
hostile greedy 568 ms 0 resets, 1000 escapes
hostile adaptive 607 ms 0 resets, 1000 escapes, 11 skipped (+7%)
mixed greedy 1981 ms 17 resets, 1983 escapes
mixed adaptive 1694 ms 14 resets, 1986 escapes, 2 skipped (-17%)
Adaptive wins on friendly (-6%) and mixed (-17%, the policy's
design target). On fully hostile workloads implicit GC fires 982
of 1000 arenas before the dispatcher sees them, so the signal is
drowned and greedy happens to edge adaptive by ~7%. Section
explicitly calls out the collaborative-but-local structure
(shared state on arena_active + EMA + countdown, decisions made
locally by each component) and credits the benchmark work with
surfacing two real correctness bugs in the conservative stack
scan — 24-byte strings misread as env nodes, 40-byte strings
misread as 25-element vectors — both now fixed.
Also:
- meta-gc-policy.dot rewritten to show the adaptive gate
(rate > 50% + probe countdown) before the greedy verify path;
new skip branch, new EMA annotations on edges.
- §6 reproducibility list + Makefile bench-gc-adaptive target.
- PDF rebuilt at 2.64 MB.
137 asm no-GC + 137 asm GC + 189 shared functional tests pass
against the new asm.
44 lines
1.9 KiB
Text
44 lines
1.9 KiB
Text
// Meta-GC decision policy — 2026-04-18 (adaptive)
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// "A diagram is worth 10,000 words." — russell@unturf.com
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digraph meta_gc {
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rankdir=LR
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node [shape=box, style="filled,rounded", fontname="Helvetica", fontsize=10]
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edge [fontname="Helvetica", fontsize=9]
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label="Meta-GC decision at (with-arena thunk) exit — adaptive + greedy layers"
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labelloc=t
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fontsize=13
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fontname="Helvetica Bold"
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enter [label="Arena enter\nsnapshot %r15\nactive ← 1\nfreelist OFF" fillcolor="#fff3cd"]
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thunk [label="Run thunk\n(apply_proc_raw)\nzero volatile regs" fillcolor="#d4edda"]
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gate1 [label="arena_active\nstill 1?" shape=diamond fillcolor="#fab1a0"]
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abort [label="SKIP reset\n(implicit GC ran)\nEMA += escape" fillcolor="#fab1a0"]
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gate_rate [label="adaptive mode\n& rate > 50%?" shape=diamond fillcolor="#ffd6a5"]
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gate_probe [label="probe\ncountdown > 0?" shape=diamond fillcolor="#ffd6a5"]
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skip [label="SKIP verify\nlet heap grow\nnext overflow → full GC\nEMA += escape" fillcolor="#fd9644"]
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verify [label="Verify\nmark phase\n(globals, syms,\nstack, + result)" fillcolor="#81ecec"]
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gate2 [label="Mark in\n[snap, r15)?" shape=diamond fillcolor="#81ecec"]
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reset [label="BULK RESET O(1)\n%r15 ← snap\nresets++\nEMA += 0" fillcolor="#00b894" fontcolor=white]
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escape [label="SWEEP FALLBACK\ngc_sweep full\nescapes++\nEMA += 1" fillcolor="#e17055" fontcolor=white]
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ret [label="Return result\n(arena-stats)" fillcolor="#dfe6e9"]
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enter -> thunk -> gate1
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gate1 -> gate_rate [label="yes"]
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gate1 -> abort [label="no"]
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gate_rate -> verify [label="no (rate low\nor greedy)"]
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gate_rate -> gate_probe [label="yes"]
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gate_probe -> skip [label="yes\n(-- countdown)"]
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gate_probe -> verify [label="no (probe,\nreset countdown)"]
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verify -> gate2
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gate2 -> reset [label="no"]
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gate2 -> escape [label="yes"]
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reset -> ret
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escape -> ret
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skip -> ret
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abort -> ret
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}
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