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This script allocates blocks of memory and uses System.GC.GetTotalMemory to assess how much memory was reserved with each allocation. It appears that the Mono heap (at least in Windows 64-bit Editor and standalone build, as of Unity 5.4.3f1) always allocates memory in multiples of 4096 bytes.

More info in this forum post.


To try this for yourself:

  1. Copy the script into your project.
  2. Add a TestGC component to any active object in your scene.
  3. Run the memory from the context menu in the Inspector, or from the run-time GUI.

Note that results are logged with Debug.Log, not displayed on screen.


/// Test program for GC.GetTotalMemory.
/// Yossarian King / Blackbird Interactive Inc. / December 2016
/// No form of copyright asserted, use as you see fit.
using System;
using System.Collections.Generic;
using UnityEngine;
public class TestGC : MonoBehaviour
    // (4096 - 40) causes 4096 byte allocation per block; +1 will allocate 8192 bytes per block
    // (1024 - 40) causes 4096 byte allocation per every 4  blocks; +1 will allocate 4096 bytes every 3 blocks
    // Smaller blocks (e.g. 512 and below) still show the 4K deltas, but the overhead seems to be higher, not sure why?
    // Results are consistent between 64-bit Unity Editor (edit time or  play mode) and x64 Windows standalone build.
    // Tested with Unity 5.4.3f1.
    [SerializeField]int BlockSize = 4056;
    [SerializeField]int BlockCount = 100;
    [SerializeField]bool ForceCollection = false;
    // GUI method to do the test while running.
    private void OnGUI()
        if (GUILayout.Button("TestTotalMemory"))
        GUILayout.Label("Block Size:");
        BlockSize = Int32.Parse(GUILayout.TextField(BlockSize.ToString()));
        GUILayout.Label("Block Count:");
        BlockCount = Int32.Parse(GUILayout.TextField(BlockCount.ToString()));
    // Context menu to do the test from editor (via Inspector context menu).
    private void TestTotalMemory()
        byte[][] blocks = new byte[BlockCount][];
        long[] blockMemoryDiff = new long[BlockCount];
        long previousTotalMemory = GetTotalMemory();
        for (int i = 0; i < BlockCount; ++i)
            blocks[i] = new byte[BlockSize];
            long newTotalMemory = GetTotalMemory();
            blockMemoryDiff[i] = newTotalMemory - previousTotalMemory;
            previousTotalMemory = newTotalMemory;
        Debug.LogFormat("=== BLOCK SIZE {0}; BLOCK COUNT {1} ===", BlockSize, BlockCount);
        long sumOfBlocks = 0;
        for (int i = 0; i < BlockCount; ++i)
            sumOfBlocks += BlockSize;
            if (blockMemoryDiff[i] != 0)
                Debug.LogFormat("{0}: diff={1} (expected={2})", i, blockMemoryDiff[i], sumOfBlocks);
                sumOfBlocks = blocks[i][0];     // HACK: reference an element in a block to make sure GC can't reclaim it before we gather allocation data.
    private long GetTotalMemory()
        if (ForceCollection)
            // Wasn't sure if passing flag to GetTotalMemory has the same effect, so just in case ...
        return System.GC.GetTotalMemory(ForceCollection);
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