Start mimalloc's scavenger thread explicitly at startup

scripts/build/deps/mimalloc.ts

@@ -12,7 +12,7 @@
 
 import type { Dependency, DirectBuild } from "../source.ts";
 
-const MIMALLOC_COMMIT = "24211c6e7610ae7c4ec06040758ec90bd21a1c83";
+const MIMALLOC_COMMIT = "65b95f778e21fb4f317a87a66426024b9b83d1f7";
 
 export const mimalloc: Dependency = {
   name: "mimalloc",

src/bun_bin/lib.rs

@@ -170,6 +170,11 @@ pub unsafe extern "C" fn main(argc: c_int, argv: *const *const c_char) -> c_int
         libc::signal(libc::SIGXFSZ, libc::SIG_IGN);
     }
 
+    // 1.5. Start mimalloc's background scavenger thread. mimalloc leaves
+    //      that to the application instead of spawning it during process
+    //      init; after the signal setup above so it stays single-threaded.
+    bun_alloc::mimalloc::mi_scavenger_start();
+
     // Windows-only startup. Must run BEFORE the first libuv
     // call (uv allocator) and before anything reads `Bun.env`/`process.env`
     // (env conversion).

src/mimalloc_sys/mimalloc.rs

@@ -57,6 +57,10 @@ unsafe extern "C" {
     /// free blocks inside its still-used pages, and hands the arena purge to the scavenger.
     /// Safe on any thread; a no-op on a thread that never allocated. No preconditions.
     pub safe fn mi_on_thread_idle();
+    /// Start the background scavenger thread that purges freed arena memory off-thread.
+    /// mimalloc does not start it on its own; until this is called purging stays
+    /// allocation-driven. Idempotent; no preconditions.
+    pub safe fn mi_scavenger_start();
     /// No preconditions.
     pub safe fn mi_version() -> c_int;
     /// No preconditions.

test/js/node/process/process.test.js

@@ -333,7 +333,7 @@ it("process.versions", () => {
   const expectedVersions = {
     boringssl: "1a41b9025c2c0a37edd07ff10f6944f03e028522",
     libarchive: "ded82291ab41d5e355831b96b0e1ff49e24d8939",
-    mimalloc: "24211c6e7610ae7c4ec06040758ec90bd21a1c83",
+    mimalloc: "65b95f778e21fb4f317a87a66426024b9b83d1f7",
     picohttpparser: "066d2b1e9ab820703db0837a7255d92d30f0c9f5",
     zlib: "12731092979c6d07f42da27da673a9f6c7b13586",
     tinycc: "12882eee073cfe5c7621bcfadf679e1372d4537b",