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perf(allocator): increase initial chunk size from 512B to 16KB (#18234)

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## Summary

- Increase `FIRST_ALLOCATION_GOAL` from 512 bytes to 16 KB to reduce malloc calls
- Fix `Bump::with_capacity()` to respect exact capacity requested (otherwise `with_capacity(1024)` would allocate 16KB)

## Malloc Reduction

Tested against 310K real-world JS/TS files:

| Dataset | Files | Before (avg mallocs) | After | Reduction |
|---------|-------|---------------------|-------|-----------|
| oxlint-ecosystem-ci | 256K | 10.99 | 7.72 | **30%** |
| monitor-oxc npm | 53K | 11.56 | 8.51 | **26%** |

Memory overhead increases by ~37% in allocated capacity, but actual memory *used* remains the same since AST size does not change.

## Parser Benchmark (vs main)

| File | Size | Change |
|------|------|--------|
| RadixUIAdoptionSection.jsx | 2.5 KB | **-5.14%** ✅ |
| cal.com.tsx | 1 MB | **-4.85%** ✅ |
| react.development.js | 84 KB | -0.19% |
| binder.ts | 193 KB | -0.53% |
| checker.ts | 2.9 MB | -0.03% |

Smaller/medium files show ~5% speedup from fewer malloc calls.

🤖 Generated with [Claude Code](https://claude.ai/code)
This commit is contained in:
Boshen committed 2026-01-19 14:45:54 +00:00
1 parent 2ef5647495
commit 2349031fbf
3 files changed
+7 -9
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crates/oxc_allocator/src/bump.rs
+3 -5
View File
@@ -487,10 +487,8 @@ const MALLOC_OVERHEAD: usize = 16;
// nearest suitable size boundary.
const OVERHEAD: usize = (MALLOC_OVERHEAD + FOOTER_SIZE + (CHUNK_ALIGN - 1)) & !(CHUNK_ALIGN - 1);
// Choose a relatively small default initial chunk size, since we double chunk
// sizes as we grow bump arenas to amortize costs of hitting the global
// allocator.
const FIRST_ALLOCATION_GOAL: usize = 1 << 9;
// 16KB covers the majority of real-world JS/TS files and reduces malloc calls by ~30%.
const FIRST_ALLOCATION_GOAL: usize = 1 << 14;
// The actual size of the first allocation is going to be a bit smaller
// than the goal. We need to make room for the footer, and we also need
@@ -575,7 +573,7 @@ impl Bump {
let chunk_footer = unsafe {
Self::new_chunk(
Bump::new_chunk_memory_details(None, layout).ok_or(AllocErr)?,
Bump::new_chunk_memory_details(Some(capacity), layout).ok_or(AllocErr)?,
layout,
EMPTY_CHUNK.get(),
)
tasks/track_memory_allocations/allocs_minifier.snap
+3 -3
View File
@@ -4,11 +4,11 @@ checker.ts | 2.92 MB || 4128 | 1669 |
cal.com.tsx | 1.06 MB || 21098 | 474 || 37138 | 4586
RadixUIAdoptionSection.jsx | 2.52 kB || 65 | 3 || 30 | 6
RadixUIAdoptionSection.jsx | 2.52 kB || 58 | 3 || 30 | 6
pdf.mjs | 567.30 kB || 4691 | 569 || 47464 | 7730
antd.js | 6.69 MB || 10732 | 2514 || 331644 | 69358
antd.js | 6.69 MB || 10728 | 2514 || 331644 | 69358
binder.ts | 193.08 kB || 431 | 119 || 7075 | 824
binder.ts | 193.08 kB || 430 | 119 || 7075 | 824
tasks/track_memory_allocations/allocs_semantic.snap
+1 -1
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@@ -4,7 +4,7 @@ checker.ts | 2.92 MB || 2166 | 1015 |
cal.com.tsx | 1.06 MB || 14986 | 208 || 0 | 0
RadixUIAdoptionSection.jsx | 2.52 kB || 23 | 0 || 0 | 0
RadixUIAdoptionSection.jsx | 2.52 kB || 21 | 0 || 0 | 0
pdf.mjs | 567.30 kB || 1756 | 284 || 0 | 0