worker: add flag to control old space size

This adds a new flag `--thread-max-old-space-size` (name completely
provisional). This has two advantages over the existing
`--max-old-space-size` flag:

1. It allows setting the old space size for the main thread and using
   `resourceLimits` for worker threads. Currently `resourceLimits` will
   be ignored when `--max-old-space-size` is set (see the attached
   issues).
2. It is implemented using V8's public API, rather than relying on V8's
   internal flags whose stability and functionality are not guaranteed.

The downside is that there are now two flags which (in most cases) do
the same thing, so it may cause some confusion. I also think that we
should deprecate `--max-old-space-size`, since the semantics feel pretty
error-prone, but that's a story for another day.

Refs: nodejs#41066
Refs: nodejs#43991
Refs: nodejs#43992

doc/api/cli.md

@@ -1117,6 +1117,20 @@ added: v18.0.0
 Configures the test runner to only execute top level tests that have the `only`
 option set.
 
+### `--thread-max-old-space-size`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Sets the max memory size of V8's old memory section for the main thread (in
+megabytes). As memory consumption approaches the limit, V8 will spend more time
+on garbage collection in an effort to free unused memory.
+
+Unlike [`--max-old-space-size`][], this option doesn't affect any additional
+[worker threads][]. To configure the old space size for worker threads, pass in
+an appropriate [`resourceLimits`][] to their constructor.
+
 ### `--throw-deprecation`
 
 <!-- YAML
@@ -1710,6 +1724,7 @@ Node.js options that are allowed are:
 * `--secure-heap-min`
 * `--secure-heap`
 * `--test-only`
+* `--thread-max-old-space-size`
 * `--throw-deprecation`
 * `--title`
 * `--tls-cipher-list`
@@ -2042,6 +2057,9 @@ Sets the max memory size of V8's old memory section. As memory
 consumption approaches the limit, V8 will spend more time on
 garbage collection in an effort to free unused memory.
 
+Unlike [`--thread-max-old-space-size`][], this sets the max old space size of
+all [worker threads][].
+
 On a machine with 2 GiB of memory, consider setting this to
 1536 (1.5 GiB) to leave some memory for other uses and avoid swapping.
 
@@ -2093,8 +2111,10 @@ done
 [`--diagnostic-dir`]: #--diagnostic-dirdirectory
 [`--experimental-wasm-modules`]: #--experimental-wasm-modules
 [`--heap-prof-dir`]: #--heap-prof-dir
+[`--max-old-space-size`]: #--max-old-space-sizesize-in-megabytes
 [`--openssl-config`]: #--openssl-configfile
 [`--redirect-warnings`]: #--redirect-warningsfile
+[`--thread-max-old-space-size`]: #--thread-max-old-space-size
 [`Atomics.wait()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait
 [`Buffer`]: buffer.md#class-buffer
 [`CRYPTO_secure_malloc_init`]: https://www.openssl.org/docs/man1.1.0/man3/CRYPTO_secure_malloc_init.html
@@ -2107,6 +2127,7 @@ done
 [`dnsPromises.lookup()`]: dns.md#dnspromiseslookuphostname-options
 [`import` specifier]: esm.md#import-specifiers
 [`process.setUncaughtExceptionCaptureCallback()`]: process.md#processsetuncaughtexceptioncapturecallbackfn
+[`resourceLimits`]: worker_threads.md#new-workerfilename-options
 [`tls.DEFAULT_MAX_VERSION`]: tls.md#tlsdefault_max_version
 [`tls.DEFAULT_MIN_VERSION`]: tls.md#tlsdefault_min_version
 [`unhandledRejection`]: process.md#event-unhandledrejection
@@ -2126,3 +2147,4 @@ done
 [semi-space]: https://www.memorymanagement.org/glossary/s.html#semi.space
 [timezone IDs]: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
 [ways that `TZ` is handled in other environments]: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html
+[worker threads]: worker_threads.md

doc/node.1

@@ -391,6 +391,11 @@ Starts the Node.js command line test runner.
 Configures the test runner to only execute top level tests that have the `only`
 option set.
 .
+.It Fl -thread-max-old-space-size
+Sets the max memory size of V8's old memory section for the main thread (in
+megabytes). As memory consumption approaches the limit, V8 will spend more time
+on garbage collection in an effort to free unused memory.
+.
 .It Fl -throw-deprecation
 Throw errors for deprecations.
 .

src/api/environment.cc

@@ -330,7 +330,9 @@ IsolateData* CreateIsolateData(Isolate* isolate,
                                uv_loop_t* loop,
                                MultiIsolatePlatform* platform,
                                ArrayBufferAllocator* allocator) {
-  return new IsolateData(isolate, loop, platform, allocator);
+  auto options = std::make_shared<PerIsolateOptions>(
+      *(per_process::cli_options->per_isolate));
+  return new IsolateData(isolate, loop, std::move(options), platform, allocator);
 }
 
 void FreeIsolateData(IsolateData* isolate_data) {

src/env.cc

@@ -367,17 +367,16 @@ void IsolateData::CreateProperties() {
 
 IsolateData::IsolateData(Isolate* isolate,
                          uv_loop_t* event_loop,
+                         std::shared_ptr<PerIsolateOptions> options,
                          MultiIsolatePlatform* platform,
                          ArrayBufferAllocator* node_allocator,
                          const std::vector<size_t>* indexes)
     : isolate_(isolate),
       event_loop_(event_loop),
+      options_(options),
       node_allocator_(node_allocator == nullptr ? nullptr
                                                 : node_allocator->GetImpl()),
       platform_(platform) {
-  options_.reset(
-      new PerIsolateOptions(*(per_process::cli_options->per_isolate)));
-
   if (indexes == nullptr) {
     CreateProperties();
   } else {

src/env.h

@@ -579,6 +579,7 @@ class NODE_EXTERN_PRIVATE IsolateData : public MemoryRetainer {
  public:
   IsolateData(v8::Isolate* isolate,
               uv_loop_t* event_loop,
+              std::shared_ptr<PerIsolateOptions> options,
               MultiIsolatePlatform* platform = nullptr,
               ArrayBufferAllocator* node_allocator = nullptr,
               const std::vector<size_t>* indexes = nullptr);
@@ -642,9 +643,9 @@ class NODE_EXTERN_PRIVATE IsolateData : public MemoryRetainer {
 
   v8::Isolate* const isolate_;
   uv_loop_t* const event_loop_;
+  std::shared_ptr<PerIsolateOptions> options_;
   NodeArrayBufferAllocator* const node_allocator_;
   MultiIsolatePlatform* platform_;
-  std::shared_ptr<PerIsolateOptions> options_;
   worker::Worker* worker_context_ = nullptr;
 };
 

src/node_main_instance.cc

@@ -40,8 +40,10 @@ NodeMainInstance::NodeMainInstance(Isolate* isolate,
       platform_(platform),
       isolate_data_(nullptr),
       snapshot_data_(nullptr) {
-  isolate_data_ =
-      std::make_unique<IsolateData>(isolate_, event_loop, platform, nullptr);
+  auto options = std::make_shared<PerIsolateOptions>(
+      *(per_process::cli_options->per_isolate));
+  isolate_data_ = std::make_unique<IsolateData>(
+      isolate_, event_loop, std::move(options), platform, nullptr);
 
   SetIsolateMiscHandlers(isolate_, {});
 }
@@ -77,20 +79,33 @@ NodeMainInstance::NodeMainInstance(const SnapshotData* snapshot_data,
 
   isolate_ = Isolate::Allocate();
   CHECK_NOT_NULL(isolate_);
+
+  auto options = std::make_shared<PerIsolateOptions>(
+      *(per_process::cli_options->per_isolate));
+
   // Register the isolate on the platform before the isolate gets initialized,
   // so that the isolate can access the platform during initialization.
   platform->RegisterIsolate(isolate_, event_loop);
   SetIsolateCreateParamsForNode(isolate_params_.get());
+
+  size_t thread_max_old_space_size = options->thread_max_old_space_size;
+  if (thread_max_old_space_size != 0) {
+    isolate_params_->constraints.set_max_old_generation_size_in_bytes(
+        thread_max_old_space_size * 1024 * 1024);
+  }
+
   Isolate::Initialize(isolate_, *isolate_params_);
 
   // If the indexes are not nullptr, we are not deserializing
   isolate_data_ = std::make_unique<IsolateData>(
       isolate_,
       event_loop,
+      std::move(options),
       platform,
       array_buffer_allocator_.get(),
       snapshot_data == nullptr ? nullptr
                                : &(snapshot_data->isolate_data_indices));
+
   IsolateSettings s;
   SetIsolateMiscHandlers(isolate_, s);
   if (snapshot_data == nullptr) {

src/node_options.cc

@@ -657,6 +657,12 @@ PerIsolateOptionsParser::PerIsolateOptionsParser(
             &PerIsolateOptions::track_heap_objects,
             kAllowedInEnvironment);
 
+  AddOption(
+      "--thread-max-old-space-size",
+      "set the maximum old space heap size (in megabytes) for this isolate",
+      &PerIsolateOptions::thread_max_old_space_size,
+      kAllowedInEnvironment);
+
   // Explicitly add some V8 flags to mark them as allowed in NODE_OPTIONS.
   AddOption("--abort-on-uncaught-exception",
             "aborting instead of exiting causes a core file to be generated "

src/node_options.h

@@ -207,6 +207,7 @@ class PerIsolateOptions : public Options {
   bool report_uncaught_exception = false;
   bool report_on_signal = false;
   bool experimental_shadow_realm = false;
+  size_t thread_max_old_space_size = 0;
   std::string report_signal = "SIGUSR2";
   inline EnvironmentOptions* get_per_env_options();
   void CheckOptions(std::vector<std::string>* errors) override;

test/common/allocate-and-check-limits.js

@@ -0,0 +1,34 @@
+'use strict';
+const assert = require('assert');
+const v8 = require('v8');
+
+function allocateUntilCrash(resourceLimits) {
+  const array = [];
+  while (true) {
+    const usedMB = v8.getHeapStatistics().used_heap_size / 1024 / 1024;
+    const maxReservedSize = resourceLimits.maxOldGenerationSizeMb +
+                            resourceLimits.maxYoungGenerationSizeMb;
+    assert(usedMB < maxReservedSize);
+
+    let seenSpaces = 0;
+    for (const { space_name, space_size } of v8.getHeapSpaceStatistics()) {
+      if (space_name === 'new_space') {
+        seenSpaces++;
+        assert(
+          space_size / 1024 / 1024 < resourceLimits.maxYoungGenerationSizeMb * 2);
+      } else if (space_name === 'old_space') {
+        seenSpaces++;
+        assert(space_size / 1024 / 1024 < resourceLimits.maxOldGenerationSizeMb);
+      } else if (space_name === 'code_space') {
+        seenSpaces++;
+        assert(space_size / 1024 / 1024 < resourceLimits.codeRangeSizeMb);
+      }
+    }
+    assert.strictEqual(seenSpaces, 3);
+
+    for (let i = 0; i < 100; i++)
+      array.push([array]);
+  }
+}
+
+module.exports = { allocateUntilCrash };

test/fixtures/thread-max-old-space-size.js

@@ -0,0 +1,3 @@
+const { allocateUntilCrash } = require('../common/allocate-and-check-limits');
+const resourceLimits = JSON.parse(process.argv[2]);
+allocateUntilCrash(resourceLimits);

test/parallel/test-thread-max-old-space-size.js

@@ -0,0 +1,16 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const fixtures = require('../common/fixtures');
+const fixture = fixtures.path('thread-max-old-space-size.js');
+const { spawnSync } = require('child_process');
+const resourceLimits = {
+  maxOldGenerationSizeMb: 16,
+  maxYoungGenerationSizeMb: 4,
+  // Set codeRangeSizeMb really high to effectively ignore it.
+  codeRangeSizeMb: 999999,
+  stackSizeMb: 4,
+};
+const res = spawnSync(process.execPath, [`--stack-size=${1024 * resourceLimits.stackSizeMb}`, `--thread-max-old-space-size=${resourceLimits.maxOldGenerationSizeMb}`, `--max-semi-space-size=${resourceLimits.maxYoungGenerationSizeMb / 2}`, fixture, JSON.stringify(resourceLimits)]);
+assert(res.stderr.toString('utf8').includes('Allocation failed - JavaScript heap out of memory'));

test/parallel/test-worker-max-old-space-size.js

@@ -0,0 +1,35 @@
+// Flags: --thread-max-old-space-size=1024
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { Worker, resourceLimits } = require('worker_threads');
+const { allocateUntilCrash } = require('../common/allocate-and-check-limits');
+
+const testResourceLimits = {
+  maxOldGenerationSizeMb: 16,
+  maxYoungGenerationSizeMb: 4,
+  codeRangeSizeMb: 16,
+  stackSizeMb: 1,
+};
+
+// Do not use isMainThread so that this test itself can be run inside a Worker.
+if (!process.env.HAS_STARTED_WORKER) {
+  process.env.HAS_STARTED_WORKER = 1;
+  const w = new Worker(__filename, { resourceLimits: testResourceLimits });
+  assert.deepStrictEqual(w.resourceLimits, testResourceLimits);
+  w.on('exit', common.mustCall((code) => {
+    assert.strictEqual(code, 1);
+    assert.deepStrictEqual(w.resourceLimits, {});
+  }));
+  w.on('error', common.expectsError({
+    code: 'ERR_WORKER_OUT_OF_MEMORY',
+    message: 'Worker terminated due to reaching memory limit: ' +
+    'JS heap out of memory'
+  }));
+  return;
+}
+
+assert.deepStrictEqual(resourceLimits, testResourceLimits);
+// resourceLimits should be used; --thread-max-old-space-size should only
+// affect the main thread.
+allocateUntilCrash(resourceLimits);

test/parallel/test-worker-resource-limits.js

@@ -1,8 +1,8 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
-const v8 = require('v8');
 const { Worker, resourceLimits, isMainThread } = require('worker_threads');
+const { allocateUntilCrash } = require('../common/allocate-and-check-limits');
 
 if (isMainThread) {
   assert.deepStrictEqual(resourceLimits, {});
@@ -33,29 +33,4 @@ if (!process.env.HAS_STARTED_WORKER) {
 }
 
 assert.deepStrictEqual(resourceLimits, testResourceLimits);
-const array = [];
-while (true) {
-  const usedMB = v8.getHeapStatistics().used_heap_size / 1024 / 1024;
-  const maxReservedSize = resourceLimits.maxOldGenerationSizeMb +
-                          resourceLimits.maxYoungGenerationSizeMb;
-  assert(usedMB < maxReservedSize);
-
-  let seenSpaces = 0;
-  for (const { space_name, space_size } of v8.getHeapSpaceStatistics()) {
-    if (space_name === 'new_space') {
-      seenSpaces++;
-      assert(
-        space_size / 1024 / 1024 < resourceLimits.maxYoungGenerationSizeMb * 2);
-    } else if (space_name === 'old_space') {
-      seenSpaces++;
-      assert(space_size / 1024 / 1024 < resourceLimits.maxOldGenerationSizeMb);
-    } else if (space_name === 'code_space') {
-      seenSpaces++;
-      assert(space_size / 1024 / 1024 < resourceLimits.codeRangeSizeMb);
-    }
-  }
-  assert.strictEqual(seenSpaces, 3);
-
-  for (let i = 0; i < 100; i++)
-    array.push([array]);
-}
+allocateUntilCrash(resourceLimits);