From e46b2e5e32319ced9a67c5f3f16804b54aa78ffa Mon Sep 17 00:00:00 2001
From: Adrien Maret <adrien@maret.email>
Date: Tue, 29 Dec 2020 15:36:41 +0100
Subject: [PATCH] process: add direct access to rss without iterating pages
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Accessing the rss value through memoryUsage() can be expensive
because this method will also generate  memory usage statistics
by iterating on each page.
This commit intend to offer a more direct access to rss value.

Refs: #33384

PR-URL: https://github.com/nodejs/node/pull/34291
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 doc/api/process.md                 | 22 ++++++++++++++++++++++
 lib/internal/process/per_thread.js |  3 +++
 src/node_process_methods.cc        | 14 +++++++++++++-
 test/parallel/test-memory-usage.js |  2 ++
 4 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/doc/api/process.md b/doc/api/process.md
index 6eaf5b511323c9..ca073b9ed56e8e 100644
--- a/doc/api/process.md
+++ b/doc/api/process.md
@@ -1610,6 +1610,28 @@ 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
diff --git a/lib/internal/process/per_thread.js b/lib/internal/process/per_thread.js
index b8f03ffef1939b..a0132a955d650a 100644
--- a/lib/internal/process/per_thread.js
+++ b/lib/internal/process/per_thread.js
@@ -46,6 +46,7 @@ function wrapProcessMethods(binding) {
     hrtimeBigInt: _hrtimeBigInt,
     cpuUsage: _cpuUsage,
     memoryUsage: _memoryUsage,
+    rss,
     resourceUsage: _resourceUsage
   } = binding;
 
@@ -160,6 +161,8 @@ function wrapProcessMethods(binding) {
     };
   }
 
+  memoryUsage.rss = rss;
+
   function exit(code) {
     if (code || code === 0)
       process.exitCode = code;
diff --git a/src/node_process_methods.cc b/src/node_process_methods.cc
index 29950aeb5b1680..69e910a8598881 100644
--- a/src/node_process_methods.cc
+++ b/src/node_process_methods.cc
@@ -193,7 +193,7 @@ 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;
@@ -201,6 +201,12 @@ static void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
   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;
@@ -213,6 +219,11 @@ 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();
@@ -450,6 +461,7 @@ 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, "hrtime", Hrtime);
   env->SetMethod(target, "hrtimeBigInt", HrtimeBigInt);
diff --git a/test/parallel/test-memory-usage.js b/test/parallel/test-memory-usage.js
index e8743c47d235c0..609244f5fc07fc 100644
--- a/test/parallel/test-memory-usage.js
+++ b/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);