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[JSC] AOT: remove the address space ballast - #937
Under RLIMIT_AS, a compiled executable reserved 8 MB of unused address space and released it 1 MB at a time when an infallible malloc failed, so that the thread could reach a point where it throws a RangeError. Making that work needed hooks throughout mimalloc (ten patches in oven-sh/bun), and it was still best effort: a request larger than what was left of the reserve crashed anyway.
This removes it. An infallible malloc that fails crashes on purpose again, as it does without compiled code and in upstream JavaScriptCore. Fallible allocations (strings, arrays, typed arrays, ArrayBuffer) still throw a RangeError.
What stays
The cage reserved in segments under a limit
unchanged
The reserve of the cage, and the RangeError at the object limit
unchanged
The reserve of the structure heap
unchanged
new Worker() failing cleanly when there is no room for another thread
unchanged
Changes
Where
What
bmalloc.{h,cpp}
The ballast API and the retries in malloc, zeroedMalloc, memalign, zeroedMemalign, realloc. Both files are byte for byte what they were before #914.
ExhaustedHeap::Storage, which only the ballast ever set, and RequestInExhaustedCage.
Heap, LocalAllocator, CompleteSubspace
tryUseReserveOfExhaustedCage loses its request parameter. The retry loops stay: they serve the other two reserves.
ReservedRangeHeap
addressSpaceToLeaveBesideSegment is 32 MB again.
AOTInstance
The handler, the keeper, and the wrappers around the put operations.
AOTHeapCageTests
heap-cage/ballast/* is gone. The tests for structures and storage become one test for structures alone.
14 files, +15 −1087.
Testing
Built Bun against this tree on macOS arm64 (release, local WebKit). It links, none of the removed symbols are in the binary, ordinary programs and Workers run, and a program built with bun build --compile --aot runs.
Not run:testaot (so the edited AOTHeapCageTests.cpp has not been compiled locally yet), and anything on Linux, which is the only platform where the ballast was active. CI has to cover both.
The Bun side deletes the mimalloc patches and the tests that asserted survival once address space is gone.
Under RLIMIT_AS, a compiled executable reserved 8 MB of unused address
space and released it 1 MB at a time when an infallible malloc failed, so
that the thread could reach a point where it throws a RangeError. Making
that work needed hooks throughout mimalloc (ten patches in oven-sh/bun),
and it was still best effort.
Remove it. An infallible malloc that fails crashes on purpose again, as it
does without compiled code and in upstream JavaScriptCore. Fallible
allocations still throw a RangeError.
What stays: the cage reserved in segments, the reserve of the cage, the
reserve of the structure heap, and new Worker() failing cleanly when there
is no room for another thread.
* bmalloc: drop the ballast API and the retries in malloc, zeroedMalloc,
memalign, zeroedMemalign and realloc.
* MarkedBlockCage: drop ExhaustedHeap::Storage, which only the ballast set,
and RequestInExhaustedCage.
* AOTInstance: drop the handler, the keeper and the wrappers around the put
operations.
* ExternalMimallocShims: drop the stubs for the mimalloc hooks.
* Tests: drop heap-cage/ballast/*. The tests for structures and storage
become one test for structures alone.
No actionable comments were generated in the recent review.
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Source/JavaScriptCore/heap/Heap.cpp
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Walkthrough
This change removes mimalloc address-space ballast support from bmalloc and JavaScriptCore. Heap exhaustion and reserve handling no longer include Storage ballast recovery. AOT runtime paths and tests that covered ballast behavior are updated.
Changes
Address-space ballast removal
Layer / File(s)
Summary
Remove bmalloc ballast APIs and allocation retries Source/bmalloc/bmalloc/*, Source/JavaScriptCore/shell/ExternalMimallocShims.cpp
The ballast implementation, public APIs, mimalloc allocation retry paths, and five compatibility shims are removed.
Heap allocation and reserve paths no longer use address-space ballast. ExhaustedHeap no longer includes Storage, and tryUseReserveOfExhaustedCage no longer accepts RequestInExhaustedCage.
Ballast tests are removed. A Structures-only allocator notification test replaces the combined Structures-and-Storage exhaustion tests.
Suggested reviewers: dylan-conway
Priority: Low
Merge Risk: Minimal · up to 3fbcd
No unresolved merge-blocking risk was identified in the reviewed changes.
Pre-merge checks: 4
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The title clearly and concisely identifies the primary change: removing the AOT address-space ballast.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @Source/JavaScriptCore/heap/Heap.cpp:
- Line 2943: Update Heap::tryUseReserveOfExhaustedCage to exclude
fastMallocAllocator and primitiveGigacageAllocator from the cell-cage reserve
and pending out-of-memory trap path. Keep the existing reserve handling for
eligible cage allocators; removing the ballast retry does not require routing
non-cage allocation failures through this method.
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…memory
What the reserves give back goes to the cage's own arena, where malloc cannot take it. A failed allocation of auxiliary storage spent both reserves, asked the host to end the thread, and crashed all the same.
main is at 8c6c963: #919 (simdutf base64), #936 (ICU 79.1) and #937 (the
address space ballast is removed).
Two files conflict, CLAUDE.md and JSTests/BUN-TEST-DIFFERENCES.md, in the
count of upstream tests that the fork changes. The base says 124. This
branch adds 2 (the Proxy revoke function, the RegExp legacy properties) and
#936 adds 3 (the three Intl tests with CLDR 49's text), so it is 129.
Three more files changed on both sides and merged by themselves: Dockerfile,
heap/Heap.cpp and heap/Heap.h. No .ir test of the compiler changes in this
range, and the list of numbered engine functions is the same.
…malloc to v3.6.0 and ICU to 79.1 (#47281)
Three things that go together. All three dependencies' PRs are merged,
and both pins are commits of their main branches.
| | What | From |
|---|---|---|
| 1 | The address space ballast is removed, and `patches/mimalloc/` with
it | oven-sh/WebKit#937, oven-sh/mimalloc#63 |
| 2 | mimalloc goes from v3.5.3 to v3.6.0 | oven-sh/mimalloc#64 |
| 3 | ICU goes from 78.3 to 79.1 (Unicode 18.0, CLDR 49) |
oven-sh/WebKit#936 |
**About 3:** oven-sh/WebKit#936 merged just before oven-sh/WebKit#937,
so no commit of WebKit's `main` has one without the other. It changes
some locale text (`fr` hours, `th` short time, `zh-Hant` short zone
names) and makes `EST5EDT`, `CST6CDT`, `MST7MDT` and `PST8PDT` resolve
to the zones the IANA database links them to.
What people will see, all of it CLDR 49 (an ICU 79.1 that is not Bun's
gives the same). Node has ICU 78.3, so Bun differs from Node in these
until Node moves:
| | ICU 78.3 | ICU 79.1 |
|---|---|---|
| `toLocaleDateString("ko")` | `1970. 1. 1.` | `1970/1/1` |
| `en`, `{ month: "short", year: "2-digit" }` | `Jan 70` | `Jan ’70` |
| `timeZoneName: "long"`, `Europe/London` and `Europe/Dublin` in winter,
every locale tried | `Greenwich Mean Time` | `GMT+00:00` |
| `timeZoneName: "long"`, `Pacific/Honolulu` | `Hawaii-Aleutian Standard
Time` | `Hawaii Time` |
#47314 is the same ICU upgrade by itself. The test changes here that
overlap with it are the same lines.
The `Intl` snapshots run only on the ICU version they were made with, so
they are regenerated (one value differs, the Korean date). They exist to
catch a fault in Bun's compressed ICU data, so each value was also
compared with a Node that links an ICU 79.1 whose data is not
compressed: 385 of 389 are the same, and the other 4 differ in the case
of the first letter of a display name, as they did with ICU 78.3.
## 1. The ballast and the patches
### What
**The address space ballast is removed.** Under a limit on address space
(`ulimit -v`), an executable compiled with `--aot` kept 8 MB of address
space unused. When a `malloc` that may not fail found no memory, it
released 1 MB and tried again, so that the thread could reach a point
where it throws a `RangeError`. mimalloc is not built for that, and it
took ten patches, each fixing what the one before exposed. It was still
best effort: a request larger than what was left of the reserve crashed
anyway.
Such a `malloc` crashes on purpose again, as it does in plain Bun and in
upstream JavaScriptCore. Allocations that can fail (strings, arrays,
typed arrays, `ArrayBuffer`) still throw a `RangeError`.
**`patches/mimalloc/` is gone.** We maintain a fork, so what is worth
keeping is a commit there.
| Patches | Count | Outcome |
|---|---|---|
| The ballast | 10 | Deleted |
| `hand-out-last-freed`, `hand-out-resident-slices` | 2 | Deleted, see
below |
| `new-oom-hook`, `look-in-every-bin-of-an-exclusive-arena`,
`secure-guard-pages-are-protected`, `out-of-memory-is-no-corruption` | 4
| Commits in the fork |
| `environment-sets-sizes-and-pace-only` | 1 | A generic
`MI_GETENV_ALLOWED` in the fork. The same 16 names now live in
`scripts/build/deps/mimalloc.ts`. No change in behavior. |
### What stays
The cage reserved in segments under a limit, the `RangeError` at the
object limit, the reserve of the structure heap, and `new Worker()`
throwing a `TypeError` when there is no room for another thread.
### The two `hand-out` patches
They made the allocator hand out the memory that was freed last while an
`--aot` build runs. Because `aot` is on by default, every thread-local
`mi_free` in every Bun process paid for the test: 23 → 26 instructions
on arm64, one of them a load of a global.
`bun build --compile --aot` of `typescript/lib/_tsc.js`, macOS arm64,
canary `8d5672c55`, six runs each in turn, switched off with
`MIMALLOC_HAND_OUT_LAST_FREED=0`. Min / median / max:
| | On | Off |
|---|---|---|
| Peak footprint (MB) | 553 / 585 / 676 | 523 / 530 / 542 |
| Instructions (G) | 382.2 / 382.8 / 384.3 | 381.7 / 382.6 / 383.1 |
| Cycles (G) | 175.8 / 176.8 / 182.2 | 177.7 / 179.2 / 179.9 |
| System CPU (ms) | 1171 / 1418 / 1760 | 1213 / 1457 / 1484 |
**Not measured on Linux, or on a large program.** If they show a real
gain there, they can come back as fork commits behind a define.
### Tests removed
All of them assert survival once address space is gone, which is no
longer promised.
| File | Removed |
|---|---|
| `test/aot/heap-limit-cases.ts` | 5 tests ("... where no address space
is left", "... gets back only what malloc keeps, goes on", "... shapes
of objects and of address space in one stretch ...") |
| `test/aot/workers-within-address-space-limit-cases.ts` | 5 groups, 15
cases ("... find no room at once ...", "... has taken all the room, and
the program goes on", "wave after wave ..."), and their 4 fixtures |
| `test/aot/two-builds-give-the-same-bytes.test.ts` | 1 test that used
the deleted option as its switch |
| `test/internal/build-hardened-flags.test.ts` | 1 test about the
`hand-out` patch list. The others now check the `MI_GETENV_ALLOWED`
define. |
## 2. mimalloc v3.6.0
| Change | Why |
|---|---|
| `MIMALLOC_COMMIT` | The merge of upstream `v3.6.0` into the fork |
| `purge_holes = 56` in `src/mimalloc_sys/mimalloc.rs` | The fork's
options come after upstream's, and upstream added six. 50 is now
`profile_time_interval` |
Every other option number in that enum was compared with the merged
header and is unchanged.
To go back to v3.5.3 with the same fork commits, pin
`6da53c355e1332db3161e0749111926ed35bc986` and set `purge_holes = 50`.
What differs from upstream's defaults, and why, is in
oven-sh/mimalloc#64: cache offsets only for blocks above 512 KiB, no
purge on the thread that frees, `page_reclaim_on_free` at 0.
### Memory against the previous pin
Linux x64, 64 cores, CI builds of this branch with v3.5.3 (`6da53c35`)
and with v3.6.0 at an earlier commit (`eab19c23`, before the two changes
to the defaults), 5 interleaved rounds, medians in MB. The two builds
differ in mimalloc alone.
| Workload | Peak, v3.5.3 | Peak, v3.6.0 | After going idle, v3.5.3 |
After going idle, v3.6.0 |
|---|---|---|---|---|
| Startup | 16.7 | 16.7 | 14.4 | 14.6 |
| 3M objects, 1 in 2000 kept | 583.4 | 578.9 | 96.6 | 91.4 |
| Buffers of mixed sizes | 3170.5 | 3168.9 | 33.3 | 33.0 |
| 48 MiB buffers in a loop | 66.5 | 66.3 | 18.8 | 18.7 |
| 4 waves of 16 Workers | 582.1 | 587.9 | 36.9 | 36.1 |
| `Bun.serve` under load | 54.4 | 52.6 | 32.7 | 32.4 |
| Bundling a 17 MB file | 825.7 | 810.2 | | |
The ranges of the five runs do not overlap for the bundle peak and for
the objects after going idle. The Workers peak is noise (568 to 620
against 560 to 660).
### Costs
| | v3.5.3 | v3.6.0 |
|---|---|---|
| `mi_malloc`, arm64 instructions | 22 | 23 |
| `mi_free`, arm64 instructions | 35 | 35 |
| `sizeof(mi_theap_t)` | 8240 | 8920 |
| Binary size | | +24 KB Linux x64, +48 KB macOS arm64, +114 KB Windows
x64 |
### Not measured
Speed (the machine was busy, so the timings are rough and show no
difference), memory on macOS, Windows or arm64, and a real application.
## Testing
- macOS arm64, release build against the WebKit branch: it links, none
of the removed symbols are in the binary, allocation-heavy JS and a
Worker run, a huge `ArrayBuffer` is still a catchable `RangeError`, and
a program built with `--compile --aot` runs. That build had the ballast
removed but predates the `hand-out` removal and the move to the fork
commit.
- `test/internal/build-hardened-flags.test.ts` passes (11 of 11), and
the build scripts typecheck.
- CI on the final commit (build 134939): 180 jobs passed and none
failed. That is every build lane, every Linux test job (Debian, Ubuntu
and Alpine, x64 and arm64), the 20 ASAN jobs, the hardened lane,
`cargo-test`, and Windows x64 and arm64.
- **Not run:** the macOS test jobs. No machine picked them up in any
build of this PR. The macOS build lanes pass, and the fork's own CI
passes on macOS.
- Five tests needed a retry (`testFFI`, `no-leak-records-at-exit`,
`native-contract`, `decorators`). Each needed one as often in build
134852, which is `main` with a one-line fix.
- `test/js/bun/wasm/compile-rss.test.ts` failed once and passed on retry
in an earlier build with v3.6.0 on Alpine arm64: 10.8 MiB kept against a
limit of 10. It did not in the final build. Its fixture, 24 runs per
version on Linux x64, shows no difference (idle median -0.7 against -0.8
MiB, none over the limit).
- The engine's own tests passed on Linux x64 and arm64 in
oven-sh/WebKit#937, the hardened AOT lanes among them.
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What
Under
RLIMIT_AS, a compiled executable reserved 8 MB of unused address space and released it 1 MB at a time when an infalliblemallocfailed, so that the thread could reach a point where it throws aRangeError. Making that work needed hooks throughout mimalloc (ten patches in oven-sh/bun), and it was still best effort: a request larger than what was left of the reserve crashed anyway.This removes it. An infallible
mallocthat fails crashes on purpose again, as it does without compiled code and in upstream JavaScriptCore. Fallible allocations (strings, arrays, typed arrays,ArrayBuffer) still throw aRangeError.What stays
RangeErrorat the object limitnew Worker()failing cleanly when there is no room for another threadChanges
bmalloc.{h,cpp}malloc,zeroedMalloc,memalign,zeroedMemalign,realloc. Both files are byte for byte what they were before #914.AddressSpaceBudget.h,GCSegmentedArrayInlines.h,ExternalMimallocShims.cppMarkedBlockCageExhaustedHeap::Storage, which only the ballast ever set, andRequestInExhaustedCage.Heap,LocalAllocator,CompleteSubspacetryUseReserveOfExhaustedCageloses its request parameter. The retry loops stay: they serve the other two reserves.ReservedRangeHeapaddressSpaceToLeaveBesideSegmentis 32 MB again.AOTInstanceAOTHeapCageTestsheap-cage/ballast/*is gone. The tests for structures and storage become one test for structures alone.14 files, +15 −1087.
Testing
bun build --compile --aotruns.testaot(so the editedAOTHeapCageTests.cpphas not been compiled locally yet), and anything on Linux, which is the only platform where the ballast was active. CI has to cover both.The Bun side deletes the mimalloc patches and the tests that asserted survival once address space is gone.