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deps: mimalloc to the head of bun-dev3-v2 (oven-sh/mimalloc#40, #42, #43, #44, #45, #46) - #42668
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Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review. WalkthroughThe change adds mimalloc idle-thread handoff and Windows follow-up sweep scheduling. It updates event-loop interfaces, adds timer state, pins a new mimalloc commit, and adds an integration test for large-page reclamation. Changesmimalloc idle sweeping
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LGTM — straightforward dependency pin bump following the documented pattern in scripts/build/CLAUDE.md.
What was reviewed:
- Grepped the repo for the old SHA (
ab135013…) — no stale duplicates in build scripts, CI configs, or elsewhere. MIMALLOC_COMMITconstant name is unchanged, so any workflow that seds it stays working.- Build spec is
directwith the unity TUsrc/static.c, so no hardcoded source list needs updating for this bump. - No CODEOWNERS entry covers
scripts/build/deps/; no ride-along changes to flags, defines, or patches.
Extended reasoning...
Overview
This PR changes exactly one line: the MIMALLOC_COMMIT string constant in scripts/build/deps/mimalloc.ts, moving the pin from ab13501334a8… to 64d2625acfed… on the oven-sh/mimalloc fork. No flags, defines, source lists, patches, or other build metadata are touched. The build system hashes commit + patch_contents into .ref to invalidate and re-fetch, so the bump is picked up automatically. The mimalloc build spec compiles a single unity translation unit (src/static.c), meaning upstream file additions/removals do not require source-list edits here.
Security risks
None from the diff in this repository. The change is a 40-character hex string pointing at a commit in Bun's own mimalloc fork, and the PR states the fork's CI passed 23/23 jobs (ASAN/UBSAN/TSAN/guarded builds across Linux, macOS, Windows, FreeBSD) at that commit. The upstream changes described are profiler-hook accounting fixes that are dormant until a profiler is attached, which nothing in Bun does yet. There is no injection, auth, or data-exposure surface in a commit-pin string.
Level of scrutiny
Low for the diff itself — this is the canonical "bump a dependency" edit named in scripts/build/CLAUDE.md, and version bumps are explicitly in the approvable category. The mechanical checks that matter for a pin bump were performed: the old SHA appears nowhere else in the tree, the constant name is preserved (so any sed-based update workflow keeps working), and the direct build's single-TU source list needs no update. The heavier scrutiny — allocator behavior, perf, cross-platform correctness — was applied upstream in oven-sh/mimalloc#40 and is documented at length in the PR description with instruction-count and RSS deltas well inside run-to-run noise. Green CI on all platforms remains the hard merge gate per REVIEW.md.
Other factors
No CODEOWNERS entry matches scripts/build/deps/. The PR timeline shows no prior reviews, objections, or unresolved threads. The bug hunt exited on dry_streak with no findings and no ruled-out candidates. The PR description flags a follow-up needed in the fork before a profiler is attached (mi_malloc_aligned sampling under MI_DEBUG), but explicitly notes it cannot trigger without an attached profiler and so does not affect this PR — that is future work in the fork, not a blocker here.
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Updated 6:48 PM PT - Sep 14th, 2026
✅ @Jarred-Sumner, your commit 8504798cb6a19b1ef58e5e4cdb9d3fedc537bb38 passed in 🧪 To try this PR locally: bunx bun-pr 42668That installs a local version of the PR into your bun-42668 --bun |
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
The latest push brings back an issue flagged in an earlier review; replied in that comment's thread.
Still open from earlier reviews (1):
- Unresolved: 1 minor or pre-existing.
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Actionable comments posted: 2
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Inline comments:
In `@scripts/build/deps/mimalloc.ts`:
- Line 15: Update the PR objective and validation references to use the current
MIMALLOC_COMMIT value 69050cf3ec14be4847ca3ba6c840da821fa283b0, preserving the
existing pin in the mimalloc build configuration.
In `@src/threading/ThreadPool.rs`:
- Around line 1446-1449: Reset the fallback-sweep state after idle callbacks
execute: update the Event::wait flow around drain_idle_events() so has_swept
becomes false when callbacks run, allowing a subsequent sweep before sleeping.
Preserve the existing no-scavenger handling and only reset the flag after idle
work has actually been drained.
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packages/bun-usockets/src/eventing/epoll_kqueue.cpackages/bun-usockets/src/eventing/libuv.cpackages/bun-usockets/src/internal/eventing/libuv.hscripts/build/deps/mimalloc.tssrc/jsc/bindings/BunJSCEventLoop.cppsrc/mimalloc_sys/mimalloc.rssrc/threading/ThreadPool.rssrc/uws_sys/Loop.rstest/js/bun/jsc/heapStats-mimalloc.test.ts
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Pins 64d2625acfed, the merge of oven-sh/mimalloc#40 on bun-dev3-v2. Five fixes to the sampled profiler hooks (mi_profiler_t) that came in with the upstream sync: - the small allocation that refills its page is the one that gets sampled (before, the sample went to the next allocation above 1 KiB far more often than to the size class that used up the countdown) - bytes_since_last_sample stays right when on_alloc raises the rate; a new thread's heap is sampled from its first allocation - mi_heap_destroy reports the frees of the sampled blocks it releases, and on_free of an aligned sampled block gets the pointer that on_alloc got They are what the heap profiler in #42626 needs for unbiased attribution and correct in-use accounting. Nothing in bun attaches a profiler yet: without one the change is one load and a branch on the allocator's generic path. 25 M malloc + 25 M free with bun's flags: 2.2403 G -> 2.2427 G instructions (+0.11%; 2.2463 G before the upstream sync). bun -e 1, Bun.serve, JSON and string workloads: within 0.3% of the old pin, inside the run to run spread.
…mpler) Pins 513d541960a3, the merge of oven-sh/mimalloc#43 on bun-dev3-v2, on top of #40. #40 made the allocation that refills its page the sampled one. mi_malloc_aligned with a naturally aligned size (64 bytes at 64) decides up front that it will not be sampled and then takes the plain path, so that check could turn its block into a sampled one after all, whose pointer is only 16-byte aligned: a release build freed it again inside the allocator and returned an unsampled block (1532 of 1575 samples of 200000 x mi_malloc_aligned(64, 64)), a build with MI_DEBUG asserted. An aligned request now only becomes a sample through the over-allocating path. Only reachable with a profiler attached, which nothing in bun does yet. Without a sampler: 25 M malloc + 25 M free with bun's flags execute 2.2384 G instructions (2.2403 G with main's pin, 2.2427 G at #40).
Pins 3aa0ac9bea44, the merge of oven-sh/mimalloc#42 on bun-dev3-v2, on top of #40 and #43. #42 hardens the purge pull-forward that runs when a thread goes idle (mi_on_thread_idle -> _mi_arenas_purge_now). It moved each armed arena's expire, and the sub-process expire that the purge thread sleeps on, to "now" with a load and a store. A purge pass resets both first thing, so a store based on a value read before that reset could undo it. The arena expire is now moved with a compare-and-swap, and the sub-process expire through the CAS loop that the passes use. Nothing was observed; it closes the window. 12 lines in src/arena.c, no header changes. Allocator micro benchmark: 2.2384 G instructions before and after.
Pins 58460467413a, the merge of oven-sh/mimalloc#45 on top of #44, on top of #40, #43 and #42. #44: with the profiler hooks compiled in (MI_PROFILE=1, the default) and no profiler attached, a thread paid for them in the shared page collect and extend code. A theap that does not sample now pays in the generic allocation path only, and little: hooks compiled in cost +0.2% of instructions on the allocator micro benchmark where they cost +1.5%. mi_profiler_start reaches the threads that are already running through theap->generic_fast_limit, at their next allocation that takes the generic path. #45 drops a debug assertion that raced with mi_profiler_stop. 25 M malloc + 25 M free with bun's flags: 2.2403 G instructions with main's pin, 2.2384 G with the previous commit, 2.2073 G now (-1.5% against main's pin). No header that bun includes changes.
Hole purging reaches the 4 MiB pages (blocks of 96 to 512 KiB): the purge bitmap's unit is per page, and the free blocks of a large page stay while the page is allocated from, told by an epoch that only the idle sweep moves. Adds mi_on_thread_idle_pending() to the public header; nothing bun binds changed.
…r while it sleeps One mi_on_thread_idle() no longer takes the free blocks of a 4 MiB page that the thread allocated from since its previous sweep: mimalloc keeps them for an epoch of the sweep, and a sweep ends one epoch at the most. A caller that sweeps once and then blocks for good never gives them back. The thread pool did that: a worker swept 100 ms after it ran out of work and then waited without a timeout. It now brackets that wait with mi_on_thread_idle_start()/_end(), as us_loop_run_bun_tick does around its poll, so the scavenger thread sweeps the worker's heaps while it sleeps and comes back for the large pages. Only the wait that follows a timed-out one is bracketed, so parking between tasks costs what it did. Without a scavenger the worker sweeps once inline, as before. The libuv loop on Windows cannot hand off: uv_run() dispatches completions right after its poll, inside the same call, and libuv allocates from mimalloc. It keeps its inline sweep, and while mi_on_thread_idle_pending() says blocks were left, an unref'd timer brings it back an interval later, three times at the most.
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I reviewed the expanded scope pushed since my last look (the idle-heap handoff in ThreadPool.rs, the Bun__JSC_onBeforeWait return-type change, the libuv follow-up-sweep timer, and the new FFI declarations) and didn't find any bugs. Because this now goes well beyond a pin bump — it changes allocator ownership across the event loop and worker threads on three backends, with a hard "no alloc/free between mi_on_thread_idle_start and _end" invariant — a human look at the Windows/libuv path in particular would still be worthwhile.
What was reviewed:
Bun__JSC_onBeforeWaitsignature: all three declarations (epoll_kqueue.c, libuv.c, BunJSCEventLoop.cpp) agree onunsigned int; the epoll/kqueue caller discards it explicitly and keeps its own scavenger handoff around the poll.us_loop_t↔WindowsLooplayout:idle_sweep_timerappended afteruv_check/checkin both, field order matches;us_create_loopusesus_callocso the pointer starts NULL, andus_loop_freecloses it.Event::waithandoff pairing:mi_on_thread_idle_end()runs unconditionally afterFutex::waitwheneverhanded_offis true, with only the futex syscall between them; the fallback inlinemi_on_thread_idle()is gated on!handed_off.- New test: Linux-gated, ASAN-skipped, polls RssAnon against a deadline rather than a fixed sleep, and its 12 MB bound is well under the stated 38 MB unfixed figure.
Extended reasoning...
Overview
Earlier revisions of this PR were a one-line mimalloc pin bump; the six commits since my last review add substantial behavior: worker threads in src/threading/ThreadPool.rs now hand their mimalloc heaps to the scavenger across the untimed futex wait via new mi_on_thread_idle_start/_end FFI (declared in src/mimalloc_sys/mimalloc.rs); Bun__JSC_onBeforeWait in src/jsc/bindings/BunJSCEventLoop.cpp now returns a "run again in N ms" hint that the Windows/libuv loop (packages/bun-usockets/src/eventing/libuv.c) turns into an unref'd us_timer_t stored in a new us_loop_t field mirrored in src/uws_sys/Loop.rs; and a new Linux-only RSS regression test lands in test/js/bun/jsc/heapStats-mimalloc.test.ts. The mimalloc pin moves again as well.
Security risks
None identified. No user input parsing, no auth/crypto/permissions surface. The change is internal allocator-lifecycle plumbing between the event loop, the thread pool, and mimalloc. The one safety-critical invariant is that a thread must not allocate or free between mi_on_thread_idle_start() returning true and the paired _end(); the Event::wait code keeps only a Futex::wait syscall between them with no early exits, and the SAFETY comment states the contract.
Level of scrutiny
High. This is cross-platform (epoll/kqueue vs. libuv/Windows), crosses the Rust↔C↔C++ FFI boundary with a changed return type and a mirrored struct layout, and threads an allocator-ownership handoff through hot paths (the worker-pool park loop and the per-tick event-loop entry). The libuv path in particular is Windows-only and cannot be exercised on the Linux CI lane the new test targets. That, plus the PR description still describing this as a pin-only change with "nothing else changes in bun", warrants a maintainer read of the new code rather than an automated approve.
Other factors
I have already raised the pin/description mismatch three times on earlier pushes and the author has resolved each thread, so I am not repeating that here. The concrete cross-boundary checks I ran (signature agreement across the three Bun__JSC_onBeforeWait declarations, us_loop_t/WindowsLoop field-order parity, us_calloc zero-init of idle_sweep_timer and its release in us_loop_free, start/end pairing in Event::wait) all came back clean, and the new test follows the harness conventions (poll-with-deadline, tempDir, ASAN skip, bound well below the unfixed figure).
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Without a scavenger to hand its heaps to, a worker sweeps once per wait. Idle tasks that a wake_all() makes it run in the middle of that wait free memory of their own (a bundler worker tears its arena down there); the sweep flag is cleared when any ran, so what they freed is given back before the thread sleeps for good.
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, #51): recently used large pages are left alone for a while (#42808) ## What `MIMALLOC_COMMIT` 69050cf3 → 6df7aa13, the head of `bun-dev3-v2`. Relative to main's pin that is three fork PRs: - **oven-sh/mimalloc#50**, what this PR is about: see below. - **oven-sh/mimalloc#49**: the pthread key of the allocator's thread-local slots is created once when several threads first use a second heap at the same time (macOS; the code is not compiled on Linux). Measured there: every hot path is the same instruction for instruction. - **oven-sh/mimalloc#47**: a profiler that is started again starts every thread over. Only reachable through the sampling-profiler hooks, which nothing on main calls yet; #42626 (`Bun.pprof.heap`) bumps the pin to that commit for its own sake. Whichever of the two PRs lands second keeps the newer commit, which is this one. Since #42668 the idle sweep hands back the free blocks of the allocator's 4 MiB pages (buffers of 96 KiB and up) two sweeps after the page was last allocated from, which is 100–200 ms. A server sits idle between two requests for longer than that, so it took the buffers of every request out of discarded memory again: a page fault for each 4 KiB of them, on every request. About half of that was free blocks in a page that still had a buffer in use; the other half was pages with no buffer in use at all, which were freed outright and made anew for the next request. oven-sh/mimalloc#50: a large page (its free blocks, or all of it) is left alone until it has not been allocated from for 256 epochs of the sweep, for up to 4 MiB process-wide, the pages that were used last first. There is no timer in this: an epoch ends only when some thread is swept. `MIMALLOC_PURGE_HOLES_LARGE_FLOOR=0` is the behaviour before (a bare number there is bytes: write `4MiB`, not `4096`). ## What it costs - A process in which no thread ever parks again keeps up to 4 MiB of large pages that it would have given back. Measured with the allocator alone: 24 blocks of 300 KiB, 20 freed, a few short parks and then one for good: 4460 KiB anonymous at every reading for 70 s against 1460 KiB before (3.0 MB of the 6 MB freed; a page stays or goes whole). The allocator's scavenger thread wakes for its 30 s safety timeout as before and for nothing else. - An idle server holds 0.2–1.0 MB more ten seconds after the load (3 MB after 512 KiB bodies) and the same as before a minute after. - A large application parked at a prompt: 1 MB. ## Numbers Linux x64, release builds of this tree, the mimalloc commit the only difference. `Bun.serve` that answers a request with its own body, one connection, 5 requests a second for 20 s. Minor faults of the server (`/proc/<pid>/stat`) and kernel instructions (`perf stat -e instructions:k -p`), per request: | body | main: faults | kernel instr | this PR: faults | kernel instr | |---|---|---|---|---| | 128 KiB | 65.4 | 627 K | 2.6 | 208 K | | 256 KiB | 123.9 | 1031 K | 2.5 | 375 K | | 512 KiB | 309.1 | 2331 K | 14.1 | 898 K | | `hello` | 1.1 | 128 K | 1.1 | 114 K | (No latencies: the machine was busy with other work and the median of one binary moved more from run to run than the two differ. At 512 KiB it shows through: 2.60 ms → 2.08 ms.) Idle afterwards, anonymous RSS of the server in KiB at +10 s / +70 s: 128 KiB 3128 / 2908 → 4044 / 2940; 256 KiB 3248 / 3056 → 3280 / 3044; 512 KiB 3564 / 3356 → 6624 / 3376; `hello` 2936 / 2808 → 2784 / 2780. So it holds up to 3 MB more ten seconds after the load and the same a minute after. A large `--compile`d CLI application that sits at a prompt (anonymous + file-backed RSS in MB; 10 minutes at the first prompt, a scripted session of 20 turns, 10 minutes parked; two runs each, all four started together): | | main | this PR | |---|---|---| | first prompt + 30 s | 121+95 / 122+95 | 124+67 / 124+95 | | + 2 min | 100+31 / 100+38 | 101+36 / 101+36 | | + 5 min | 96+32 / 96+38 | 97+36 / 97+37 | | + 10 min | 96+32 / 96+39 | 97+37 / 97+38 | | after the session + 30 s | 258+87 / 252+79 | 265+87 / 268+88 | | + 2 min | 190+43 / 183+44 | 197+43 / 195+44 | | + 5 min | 165+44 / 160+45 | 171+44 / 170+45 | | + 10 min | 171+51 / 166+53 | 176+52 / 176+53 | At the prompt that is 3 MB more for the first minute, 1 MB at two minutes and after. After the session these four runs are 5–10 MB apart; the same comparison with one binary and the floor switched by the environment (`…LARGE_FLOOR=0`) came out at 171 / 161 against 168 / 173 at + 5 min, so what the floor itself keeps there (3–4 MB for two minutes) is inside what two runs of one configuration differ by. Instructions (`perf stat -e instructions:u`, pinned, interleaved, median [range]): | | main | this PR | |---|---|---| | `bun -e 1` (9 runs) | 10.05 M [10.04–10.07] | 10.05 M [10.05–10.07] | | `JSON.stringify` + `JSON.parse` loop (5) | 4788.6 M [4786.5–4793.8] | 4789.3 M [4788.8–4796.6] | | allocation loop (5) | 5760.0 M [5753.6–5766.7] | 5799.9 M [5758.2–5824.1] | | the allocator alone: 50 M random `malloc`/`free` | 1.9932 G | 1.9932 G | | the allocator alone: 20 M × `malloc(128 KiB)` + `free` | 5.0313 G | 5.0313 G | (The allocation loop moves by that much between runs of one binary; its ranges overlap.) ## Test `test/js/bun/jsc/heapStats-mimalloc.test.ts`: a `Bun.serve` child that echoes 256 KiB bodies, requests 50 ms apart with the sweep's epoch shortened to 10 ms and the collector looking every 100 ms, minor faults per request read from `/proc`. 2.3–2.4 with this pin, 130–131 with main's (the bound is 20). Linux only, not ASAN.
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What does this PR do?
Moves
MIMALLOC_COMMITfromab13501334a8to69050cf3ec14be4847ca3ba6c840da821fa283b0, the head ofbun-dev3-v2: main's pin plus six merged PRs of the fork and nothing else, and changes the two callers in bun that the last of them asks to change.MI_FREE_USE_PAGEMAP=1stays.mi_heap_destroyfrees mimalloc#40: the sampled profiler hooks (mi_profiler_t) attribute a sample to the small allocation that refilled its page, keepbytes_since_last_sampleright whenon_allocraises the rate, sample a new thread's heap from its first allocation, report the frees ofmi_heap_destroy, and giveon_freeof an aligned block the pointer thaton_allocgot. What the heap profiler inBun.pprof.heap: sampling native heap profiles in pprof format #42626 needs.mi_malloc_aligned(64, 64)could free a sampled block inside the allocator;MI_DEBUGasserted).mi_on_thread_idle) goes through compare-and-swap, so it cannot undo the reset that a purge pass does first thing. 12 lines insrc/arena.c.mi_profiler_stopis gone.mincore. The bitmap's unit is now per page (16 KiB for a 4 MiB page), and the free blocks of a large page stay while the page is in use, which the allocator tells without a clock on the allocating side: the idle sweep counts epochs of 100 ms or more, an allocation from a large page leaves the current epoch in the page (a load, a compare, and a store once per epoch), and the blocks go when that is two epochs ago. Without that hold aBun.servewith 256 KiB bodies discarded and refaulted 3 GB in 20 s.Nothing in bun attaches a profiler yet. The fast paths of
mi_mallocandmi_freeare untouched by all six.include/mimalloc.hgains one function,mi_on_thread_idle_pending(), and comments;mimalloc-stats.his identical,mimalloc-profile.hdiffers in comments,mimalloc/types.hgains fields of the internalmi_theap_tandmi_tld_t. No struct or enum that bun binds changed (src/mimalloc_sys/mimalloc.rs, the declarations inBunJSCEventLoop.cppandepoll_kqueue.c).The callers that sweep once and then block
With oven-sh/mimalloc#46 ONE call of
mi_on_thread_idle()never takes the free blocks of a large page that the thread allocated from since its previous sweep: a sweep ends one epoch at the most. The event loop is fine:us_loop_run_bun_tickhands the thread's heaps to mimalloc's scavenger thread across the poll (mi_on_thread_idle_start()/_end()), and the scavenger comes back for them by itself, two or three sweeps an interval apart. Two callers swept inline once and then blocked for good, and would have kept such blocks, as they do on main:src/threading/ThreadPool.rs: a worker swept once, after its futex wait timed out at 100 ms, and then waited without a timeout. It now brackets that second wait withmi_on_thread_idle_start()/mi_on_thread_idle_end(), and sweeps inline (once, as before) only when_startsays there is no scavenger to hand off to. Nothing runs between the two calls butFutex::wait, which allocates nothing;drain_idle_eventsruns before_start.Only the wait that follows a timed-out one is bracketed. Bracketing every park was measured and is slower (table below:
_startis two read-modify-writes on cache lines that every parking thread shares, and it wakes the scavenger, which costs half a context switch per task), and sweeping on every park is what the comment there warns about (13% ofvite previewrequests per second). As it is, a worker that parks between tasks never reaches_start, andnotify()is what it was.Bun__JSC_onBeforeWaitinBunJSCEventLoop.cpp, fromus_loop_runinlibuv.c) sweeps inline at most every 100 ms and thenuv_run(UV_RUN_ONCE)blocks. It cannot hand off:uv_rundispatches the completions right after its poll inside the same call (uv__pollatsrc/win/core.c:732,uv__process_reqsat:737), and libuv allocates from mimalloc there (uv_replace_allocator), so there is no point between "about to block" and "awake" that bun's code sees without a patch to libuv. It keeps the inline sweep, and whilemi_on_thread_idle_pending()says blocks were left,Bun__JSC_onBeforeWaitreturns 100 (ms) andus_loop_runarms an unref'd timer for that long after the sweep, so the hook runs again: three times at the most after JS last ran, which is the bound the fork gives. The timer does not keep the loop alive.Not changed: when no scavenger runs (
MIMALLOC_SCAVENGER=0or a purge delay of 0; bun sets neither) the fallbacks inus_loop_run_bun_tickand in the pool sweep inline once, as on main, and the free blocks of large pages stay.How did you verify your code works?
Release builds of one tree (this branch on
04823d8fad67), Linux x64: base = main's pin, pin = this pin with the callers unchanged (the first commit), this PR = both commits.Test.
test/js/bun/jsc/heapStats-mimalloc.test.tsgains "an idle work pool thread hands back the free blocks of its large pages": a subprocess with 4 pool threads reads 480 files of 96 to 512 KiB withfs.promises.readFile(the buffers are allocated on the pool threads), keeps 1 in 12, collects the rest, and pollsRssAnonwhile nothing gives the pool work. Anonymous memory beyond what it started with and what it keeps has to come down to 12 MB within 2.5 s.BUN_GARBAGE_COLLECTOR_LEVEL=1and2, and with the system bun 1.4.1: 50 MB)The park and notify path of the pool (what the
has_sweptcomment protects). 100000await fs.promises.stat("/")one after the other (every call notifies a worker, which runs one task and parks), the same in batches of 8, andawait randomBytes(16);perf statof the whole process, 8 cores, 5 interleaved runs, medians (range):stat, sequentialstat, 8 at a timerandomBytes(16), sequentialContext switches per call are 3.96 to 3.97, 0.51 to 0.53 and 3.97 in all three, kernel instructions per call overlap (41.6 k..49.9 k sequential), wall time is within the spread of the machine.
Bracketing EVERY park instead (a build with a switch for it, 200000 calls, 4 interleaved runs), against the same build with the handoff after a timed-out wait only:
statsequential: user / kernel instructions, context switches per callstat8 at a timerandomBytes(16)sequentialstatsequentialAllocator micro benchmarks (mimalloc alone with bun's flags: clang 21,
-O3 -march=nehalem, C++,MI_FREE_USE_PAGEMAP; user-mode instructions, the runs of one build equal to within 100):mi_malloc+ 25 Mmi_freeof 16..1039 bytes707d90be)ab135013)3aa0ac9b)58460467)69050cf3)58460467to within 400 instructionsMI_PROFILE=0(not what bun builds)(The absolute numbers are 8% below the ones this description had before: the benchmark's own object file is built differently here. All rows are from one recipe.)
mi_malloc(128 KiB)+mi_free, the generic path into a large page58460467bun (5 interleaved runs pinned to 8 cores; user-mode instructions and peak RSS, medians):
bun -e 1Bun.servehello, per request (20000 sequentialfetch)Bun.servestart and stop aloneJSON.stringify+JSON.parseof a 200-user object, 3000 timesBuffer.from+split, 300 x 5000Bun.sleep), RSS / anonymous fromsmaps_rollup, binaries read into the page cache firstNothing is slower by more than 0.1% outside the spread of its own runs.
The large-buffer server of oven-sh/mimalloc#46 at bun level (
Bun.servethat reads 256 KiB request bodies and answers 90 to 270 KB of JSON; 16 connections for 15 s, then idle; RSS / anonymous fromsmaps_rollup):Under sustained load (the same server, 20 s, 3 interleaved rounds; instructions and page faults of the server process from
perf stat -p):Requests and instructions per request are the same; the buffers stay while the server is busy and go when it is not.
Tests with the release build of this PR
test/js/bun/spawn/spawn-pipe-leak.test.ts25 of 25 runs,test/js/bun/jsc/heapStats-mimalloc.test.ts(with the new test) andtest/js/bun/gc/gc-controller-cadence.test.ts10 of 10 each.require-cache,serve.test.ts, all oftest/js/web/workers,test/js/node/worker_threads,test/js/node/child_processandtest/js/node/fs(the pool-heavy ones),spawn-noread-leak,bun-file,bun-write,bundler_edgecase,esbuild/splitting. The two failures need a non-root user (the root-range port inserve.test.ts, EPERM after dropping privileges inchild_process.test.ts) and fail the same way with the base build.resolve.test.ts, want a directory that root cannot read, and fail the same way with the base build.USE_SYSTEM_BUN=1(bun 1.4.1: 50 MB) and with the first commit alone (38 to 47 MB), and passes with both.heapStats-mimalloc,gc-controller-cadenceandworker.test.tson one at58460467); the new test skips itself under ASAN, where malloc is not mimalloc.Not run here: macOS and Windows. The Windows half of the second commit (
BunJSCEventLoop.cppunderOS(WINDOWS),libuv.c,libuv.h) was compiled by nothing on this machine: the C++ function was syntax-checked withOS(WINDOWS)forced on against stubs,cargo check --target x86_64-pc-windows-msvcpasses forbun_uws_sys,bun_threadingandbun_mimalloc_sys(theWindowsLoopmirror gained the field), and the rest is for CI. The fork's CI passed 23 of 23 jobs at each of the six merges (Linux x64/arm64 with ASAN, UBSAN, TSAN and guarded builds, theMI_FREE_USE_PAGEMAPbuild that matches bun's configuration, macOS, Windows x64/arm64, FreeBSD).