Stop disabling transparent huge pages in every process bun spawns

scripts/build/deps/mimalloc.ts

@@ -12,7 +12,7 @@
 
 import type { Dependency, DirectBuild } from "../source.ts";
 
-const MIMALLOC_COMMIT = "d078ad066752ea7fd06acb2323b7a90c49d7d8e4";
+const MIMALLOC_COMMIT = "1803341d6241d8fa4b3f65fa68cb13a32ad92f04";
 
 export const mimalloc: Dependency = {
   name: "mimalloc",
@@ -54,11 +54,15 @@ export const mimalloc: Dependency = {
       ...(cfg.release && { MI_BUILD_RELEASE: true }),
     };
 
-    // Disable Transparent Huge Pages. Measured impact:
-    //   bun --eval 1:  THP off = 30MB peak,  THP on = 52MB peak
-    //   http-hello.js: THP off = 52MB peak,  THP on = 74MB peak
-    // THP trades memory for (sometimes) latency; for a JS runtime the
-    // memory cost isn't worth it. The cmake option only applies on Linux.
+    // Opt mimalloc's arenas out of Transparent Huge Pages. Only matters when
+    // /sys/kernel/mm/transparent_hugepage/enabled is `always` (RHEL, Amazon
+    // Linux, Arch); under `madvise` nothing in bun asks for huge pages anyway.
+    // Measured on an `always` box (release, x64):
+    //   bun -e 1:           THP off = 30MB peak,  THP on = 54MB peak
+    //   Bun.serve hello:    THP off = 46MB rss,   THP on = 68MB rss
+    // mimalloc does this per mapping (MADV_NOHUGEPAGE), not per process, so
+    // spawned children keep the system THP policy. JSC's reservations and
+    // bun_alloc's lazy arena opt out the same way on their side.
     if (cfg.linux) defines.MI_DEFAULT_ALLOW_THP = 0;
 
     // Skip prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ...) after each mmap.

scripts/build/deps/webkit.ts

@@ -3,7 +3,7 @@
  * for local mode. Override via `--webkit-version=<hash>` to test a branch.
  * From https://github.com/oven-sh/WebKit releases.
  */
-export const WEBKIT_VERSION = "e6e37cda216c0292ae68c30c84a9dc8601d0fba5";
+export const WEBKIT_VERSION = "ddea71318fec9b923465c7c45ded8fa713ca3251";
 
 /**
  * WebKit (JavaScriptCore) — the JS engine.

src/bun_alloc/lib.rs

@@ -1610,6 +1610,14 @@ fn bss_mmap_noreserve(len: usize) -> *mut u8 {
     if p == libc::MAP_FAILED {
         crate::out_of_memory();
     }
+    // Under THP `enabled=always` the first write to each 2 MiB stretch would
+    // fault a whole huge page, turning this demand-faulted arena into ~4 MiB of
+    // RSS. Per-VMA opt-out (not `PR_SET_THP_DISABLE`, which children inherit).
+    // SAFETY: `p..p+len` is the mapping created above.
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    unsafe {
+        libc::madvise(p, len, libc::MADV_NOHUGEPAGE);
+    }
     // LSan only scans data/BSS, stacks, and malloc-tracked heap for live
     // pointers. This anonymous mapping is none of those, so any `Box`/`Vec`
     // whose owning pointer lives inside a `bss_*!` singleton (e.g. the

test/js/bun/spawn/spawn.test.ts

@@ -7,6 +7,7 @@ import {
   getMaxFD,
   isBroken,
   isDebug,
+  isLinux,
   isMacOS,
   isPosix,
   isWindows,
@@ -1536,3 +1537,25 @@ describe("uid/gid", () => {
     expect(thrown?.code).toBe("EPERM");
   });
 });
+
+// The allocator opts its own mappings out of THP; it must not use
+// prctl(PR_SET_THP_DISABLE), which children inherit across execve. Gate on our
+// parent so an environment (or older bun) that disabled THP itself skips.
+function thpEnabled(status: string) {
+  return status.match(/^THP_enabled:\s*(\d)/m)?.[1];
+}
+function parentThp() {
+  if (!isLinux) return undefined;
+  try {
+    return thpEnabled(readFileSync(`/proc/${process.ppid}/status`, "utf8"));
+  } catch {
+    return undefined; // hidepid mount: cannot tell, skip
+  }
+}
+it.if(parentThp() === "1")("spawned children keep the system THP policy", async () => {
+  await using proc = spawn({ cmd: ["cat", "/proc/self/status"], stdout: "pipe", stderr: "inherit" });
+  const [stdout, exitCode] = await Promise.all([proc.stdout.text(), proc.exited]);
+  expect(thpEnabled(stdout)).toBe("1");
+  expect(thpEnabled(readFileSync("/proc/self/status", "utf8"))).toBe("1");
+  expect(exitCode).toBe(0);
+});

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

@@ -333,7 +333,7 @@ it("process.versions", () => {
   const expectedVersions = {
     boringssl: "1a41b9025c2c0a37edd07ff10f6944f03e028522",
     libarchive: "ded82291ab41d5e355831b96b0e1ff49e24d8939",
-    mimalloc: "d078ad066752ea7fd06acb2323b7a90c49d7d8e4",
+    mimalloc: "1803341d6241d8fa4b3f65fa68cb13a32ad92f04",
     picohttpparser: "066d2b1e9ab820703db0837a7255d92d30f0c9f5",
     zlib: "12731092979c6d07f42da27da673a9f6c7b13586",
     tinycc: "05f0fafaa3be31e31d7b4b5c17dc60f62c991171",