Antigravity Agent
150 lines
4.3 KiB
Markdown
150 lines
4.3 KiB
Markdown
---
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id: wiki-2026-0508-scavenge
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title: Scavenge
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [Minor GC, Scavenger, Young Generation GC, Cheney Scavenger]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.95
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verification_status: applied
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tags: [v8, garbage-collection, memory, runtime]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack:
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language: cpp
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framework: v8-orinoco
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---
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# Scavenge
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## 매 한 줄
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> **"매 young object 의 매 빠른 die — 매 cheap 하게 collect"**. Scavenge 는 매 generational hypothesis (most objects die young) 의 매 exploit — 매 V8 young generation 을 매 from-space / to-space 로 나누고 매 live object 만 매 to-space 로 매 copy. 매 dead object 는 매 단순 abandon. 2026 V8 (Orinoco) 에서 매 parallel + concurrent 로 매 main-thread pause < 1ms.
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## 매 핵심
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### 매 Cheney's algorithm
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1. Allocate in to-space (linear bump pointer).
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2. When full → 매 swap roles. From-space = 매 old to-space.
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3. From roots, copy 매 reachable object to (new) to-space.
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4. Update 매 forwarding pointer in from-space slot.
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5. BFS through copied objects, copying 매 referenced objects.
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6. Done → from-space 매 entirely abandoned.
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### 매 V8-specific
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- Young gen = New Space ≈ 1–8 MB per worker.
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- Promotion: 매 survives 2 scavenges → 매 Old Space.
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- Parallel Scavenge (2018+): 매 multiple threads.
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- Concurrent (2021+): root marking on background.
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### 매 응용
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1. JS heap young gen.
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2. Java HotSpot Young Generation (Parallel Scavenge collector).
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3. .NET Gen 0/1.
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4. Erlang per-process heap.
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## 💻 패턴
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### Cheney scavenge (pseudo-C)
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```c
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typedef struct { intptr_t header; void* slots[]; } Object;
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char *from, *to, *alloc;
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void* scavenge_copy(Object *obj) {
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if (is_forwarded(obj)) return forwarded_addr(obj);
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size_t size = obj_size(obj);
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Object *copy = (Object*)alloc;
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memcpy(copy, obj, size);
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alloc += size;
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set_forwarded(obj, copy);
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return copy;
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}
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void scavenge() {
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swap(&from, &to);
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alloc = to;
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char *scan = to;
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for (Root *r = roots; r; r = r->next) *r = scavenge_copy(*r);
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while (scan < alloc) {
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Object *o = (Object*)scan;
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for (int i = 0; i < slot_count(o); i++)
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o->slots[i] = scavenge_copy(o->slots[i]);
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scan += obj_size(o);
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}
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}
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```
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### Allocation (bump pointer)
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```c
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void* alloc_young(size_t bytes) {
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if (alloc + bytes > to_end) trigger_scavenge();
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void *p = alloc;
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alloc += bytes;
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return p;
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}
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```
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### Promotion check
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```c
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if (obj_age(o) >= 2) {
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void *promoted = alloc_old(obj_size(o));
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memcpy(promoted, o, obj_size(o));
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// also update remembered set if old → young pointers exist
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} else {
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scavenge_copy(o);
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inc_age(o);
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}
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```
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### Remembered set (write barrier)
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```c
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void store_field(Object *obj, int slot, Object *val) {
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obj->slots[slot] = val;
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if (in_old_space(obj) && in_young_space(val))
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remembered_set_add(&obj->slots[slot]);
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}
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```
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### V8 trace (observe scavenge)
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```bash
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node --trace-gc app.js
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# [12345:0x...] 100 ms: Scavenge 5.5 (6.7) -> 4.8 (7.7) MB, 0.4 / 0.0 ms
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```
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## 매 결정 기준
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| 상황 | Strategy |
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|---|---|
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| 매 short-lived alloc heavy | Larger young gen (--max-semi-space-size) |
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| 매 long-lived heavy | Smaller young, faster promotion |
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| 매 latency-critical | Concurrent scavenge enabled |
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| 매 throughput | Parallel scavenge |
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**기본값**: V8 default — auto-tuned per workload.
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## 🔗 Graph
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- 부모: [[Garbage Collection]] · [[V8 Engine]]
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- 변형: [[Mark-Sweep-Compact]] · [[Major GC]]
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- 응용: [[New Space(Young Generation)]] · [[Cheneys Algorithm]]
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- Adjacent: [[Orinoco GC]] · [[Stop-the-world]]
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## 🤖 LLM 활용
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**언제**: GC log analysis, allocation hotspot identification from heap snapshots, write-barrier overhead estimation.
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**언제 X**: 매 actual GC algorithm change — runtime team only.
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## ❌ 안티패턴
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- **Massive young alloc + immediate retain**: 매 promotion storm → 매 old space pressure.
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- **Linked list of small objects**: 매 scan cost 의 매 linear in slots → 매 use TypedArray.
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- **Disabling GC**: 매 --no-gc — 매 memory grows unbounded.
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## 🧪 검증 / 중복
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- Verified (V8 Orinoco docs, Cheney 1970 paper, "The Garbage Collection Handbook" 2nd Ed.).
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- 신뢰도 A.
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## 🕓 Changelog
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| 날짜 | 변경 |
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|---|---|
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — Cheney + V8 Orinoco parallel-concurrent state |
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