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perf(allocator): increase initial chunk size from 512B to 16KB #20968

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Merged
graphite-app merged 1 commit into from
Apr 2, 2026
+20 −11
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perf(allocator): increase initial chunk size from 512B to 16KB #20968

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19 changes: 14 additions & 5 deletions crates/oxc_allocator/src/bump.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -518,9 +518,10 @@ const OVERHEAD: usize = match round_up_to(MALLOC_OVERHEAD + FOOTER_SIZE, CHUNK_A
None => panic!(),
};

// The target size of our first allocation, including our overhead. The
// available bump capacity will be smaller.
const FIRST_ALLOCATION_GOAL: usize = 1 << 9;
// The target size of our first allocation, including our overhead.
// The available bump capacity will be slightly smaller.
// 16 KiB covers the majority of real-world JS/TS files.
const FIRST_ALLOCATION_GOAL: usize = 16 * 1024;

// 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 take the
Expand Down Expand Up @@ -752,7 +753,10 @@ impl<const MIN_ALIGN: usize> Bump<MIN_ALIGN> {

let chunk_footer = unsafe {
Self::new_chunk(
Self::new_chunk_memory_details(None, layout).ok_or(AllocErr)?,
// `new_size_without_footer` here was `None` in original `bumpalo` code.
// Changed to `Some(capacity)` when we increased `FIRST_ALLOCATION_GOAL` to 16 KiB,
// to avoid `Bump::with_capacity` allocating 16 KiB even when requested `capacity` is much smaller.
Self::new_chunk_memory_details(Some(capacity), layout).ok_or(AllocErr)?,
layout,
EMPTY_CHUNK.get(),
)
Expand Down Expand Up @@ -2610,7 +2614,12 @@ mod tests {
// Uses private `DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER` and `FOOTER_SIZE`.
#[test]
fn allocated_bytes() {
let mut b = Bump::with_capacity(1);
let mut b = Bump::new();

assert_eq!(b.allocated_bytes(), 0);
assert_eq!(b.allocated_bytes_including_metadata(), 0);

b.alloc(0u8);

assert_eq!(b.allocated_bytes(), DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER);
assert_eq!(
Expand Down
10 changes: 5 additions & 5 deletions tasks/track_memory_allocations/allocs_minifier.snap
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
File | File size || Sys allocs | Sys reallocs || Arena allocs | Arena reallocs | Arena bytes
-------------------------------------------------------------------------------------------------------------------------------------------
checker.ts | 2.92 MB || 334 | 37 || 152659 | 28244
checker.ts | 2.92 MB || 333 | 37 || 152659 | 28244

cal.com.tsx | 1.06 MB || 20244 | 46 || 37147 | 4570
cal.com.tsx | 1.06 MB || 20242 | 46 || 37147 | 4570

RadixUIAdoptionSection.jsx | 2.52 kB || 41 | 6 || 30 | 6
RadixUIAdoptionSection.jsx | 2.52 kB || 34 | 6 || 30 | 6

pdf.mjs | 567.30 kB || 3994 | 417 || 47464 | 7734

antd.js | 6.69 MB || 7755 | 1657 || 331673 | 69344
antd.js | 6.69 MB || 7751 | 1657 || 331673 | 69344

binder.ts | 193.08 kB || 79 | 23 || 7075 | 824
binder.ts | 193.08 kB || 78 | 23 || 7075 | 824

2 changes: 1 addition & 1 deletion tasks/track_memory_allocations/allocs_semantic.snap
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Expand Up @@ -4,7 +4,7 @@ checker.ts | 2.92 MB || 2281 | 18 |

cal.com.tsx | 1.06 MB || 14966 | 22 || 0 | 0

RadixUIAdoptionSection.jsx | 2.52 kB || 12 | 3 || 0 | 0
RadixUIAdoptionSection.jsx | 2.52 kB || 10 | 3 || 0 | 0

pdf.mjs | 567.30 kB || 1401 | 208 || 0 | 0

Expand Down
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