v8 - What do the return values of node.js process.memoryUsage() stand for?

Question

From the official documentation (source):

process.memoryUsage()

Returns an object describing the memory usage of the Node process measured in bytes.

var util = require('util');

console.log(util.inspect(process.memoryUsage()));

This will generate:

{ rss: 4935680, heapTotal: 1826816, heapUsed: 650472 }

heapTotal and heapUsed refer to V8's memory usage.

Exactly what do rss, heapTotal, and heapUsed stand for?

It might seem like a trivial question, but I've been looking and I could not find a clear answer so far.

Answer 1

In order to answer this question, one has to understand V8’s Memory Scheme first.

A running program is always represented through some space allocated in memory. This space is called Resident Set. V8 uses a scheme similar to the Java Virtual Machine and divides the memory into segments:

• Code: the actual code being executed
• Stack: contains all value types (primitives like integer or Boolean) with pointers referencing objects on the heap and pointers defining the control flow of the program
• Heap: a memory segment dedicated to storing reference types like objects, strings and closures.

Now it is easy to answer the question:

• rss: Resident Set Size
• heapTotal: Total Size of the Heap
• heapUsed: Heap actually Used

Ref: http://apmblog.dynatrace.com/2015/11/04/understanding-garbage-collection-and-hunting-memory-leaks-in-node-js/