Add direct access to rss without iterating pages

doc/api/process.md

@@ -1589,6 +1589,28 @@ Will generate:
 When using [`Worker`][] threads, `rss` will be a value that is valid for the
 entire process, while the other fields will only refer to the current thread.
 
+The `process.memoryUsage()` method iterate over each page to gather
+informations about memory usage which can be slow depending on the
+program memory allocations.
+
+## `process.memoryUsage.rss()`
+
+* Returns: {integer}
+
+The `process.memoryUsage.rss()` method returns an integer representing the
+Resident Set Size (RSS) in bytes.
+
+The Resident Set Size, is the amount of space occupied in the main
+memory device (that is a subset of the total allocated memory) for the
+process, including all C++ and JavaScript objects and code.
+
+This is the same value as the one returned by `process.memoryUsage()`.
+
+```js
+console.log(process.memoryUsage.rss());
+// 35655680
+```
+
 ## `process.nextTick(callback[, ...args])`
 <!-- YAML
 added: v0.1.26

lib/internal/process/per_thread.js

@@ -93,6 +93,7 @@ function wrapProcessMethods(binding) {
   const {
     cpuUsage: _cpuUsage,
     memoryUsage: _memoryUsage,
+    rss,
     resourceUsage: _resourceUsage
   } = binding;
 
@@ -168,6 +169,8 @@ function wrapProcessMethods(binding) {
     };
   }
 
+  memoryUsage.rss = rss;
+
   function exit(code) {
     if (code || code === 0)
       process.exitCode = code;

src/node_process_methods.cc

@@ -172,14 +172,20 @@ static void Kill(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(err);
 }
 
-static void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
+static void Rss(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
   size_t rss;
   int err = uv_resident_set_memory(&rss);
   if (err)
     return env->ThrowUVException(err, "uv_resident_set_memory");
 
+  args.GetReturnValue().Set(static_cast<double>(rss));
+}
+
+static void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+
   Isolate* isolate = env->isolate();
   // V8 memory usage
   HeapStatistics v8_heap_stats;
@@ -192,6 +198,11 @@ static void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
   Local<ArrayBuffer> ab = get_fields_array_buffer(args, 0, 5);
   double* fields = static_cast<double*>(ab->GetBackingStore()->Data());
 
+  size_t rss;
+  int err = uv_resident_set_memory(&rss);
+  if (err)
+    return env->ThrowUVException(err, "uv_resident_set_memory");
+
   fields[0] = rss;
   fields[1] = v8_heap_stats.total_heap_size();
   fields[2] = v8_heap_stats.used_heap_size();
@@ -542,6 +553,7 @@ static void InitializeProcessMethods(Local<Object> target,
   env->SetMethod(target, "umask", Umask);
   env->SetMethod(target, "_rawDebug", RawDebug);
   env->SetMethod(target, "memoryUsage", MemoryUsage);
+  env->SetMethod(target, "rss", Rss);
   env->SetMethod(target, "cpuUsage", CPUUsage);
   env->SetMethod(target, "resourceUsage", ResourceUsage);
 
@@ -568,6 +580,7 @@ void RegisterProcessMethodsExternalReferences(
   registry->Register(Umask);
   registry->Register(RawDebug);
   registry->Register(MemoryUsage);
+  registry->Register(Rss);
   registry->Register(CPUUsage);
   registry->Register(ResourceUsage);
 

test/parallel/test-memory-usage.js

@@ -44,3 +44,5 @@ if (r.arrayBuffers > 0) {
   assert.strictEqual(after.arrayBuffers - r.arrayBuffers, size,
                      `${after.arrayBuffers} - ${r.arrayBuffers} === ${size}`);
 }
+
+assert(process.memoryUsage.rss() > 0);