Large memory cannot be reclaimed

We have a large json file and after multiple deserialization there is a memory leak. I began to suspect that it was a problem with the json library(newtonsoft.json,litjson,utf8json), but it still appeared after replacing a few. So I guess whether it may be caused by too large allocated memory. Through the following code, there is indeed a situation where the memory cannot be released. Why does this happen and how to fix it. Of course, native memory can be allocated through C++, but the cost is too high. I hope the official can give some suggestions and explain the principle.

unity2020.2.6f1
The editor is normal, there will be problems after packaging the exe

Code (CSharp):

1. using System;
2. using UnityEngine;
3.  
4. public class GCTest : MonoBehaviour
5. {
6.     const int DefaultSize = 300;
7.  
8.     int MemorySize = DefaultSize;
9.     // Start is called before the first frame update
10.     void Start()
11.     {
12.         var strs = Environment.GetCommandLineArgs();
13.         if (strs.Length == 2)
14.         {
15.             if (!int.TryParse(strs[1], out MemorySize))
16.                 MemorySize = DefaultSize;
17.         }
18.     }
19.  
20.     // Update is called once per frame
21.     void Update()
22.     {
23.         if (Input.GetKeyDown(KeyCode.Space))
24.         {
25.             var bytes = new byte[1024 * 1024 * MemorySize];
26.         }
27.  
28.         if (Input.GetKeyDown(KeyCode.KeypadEnter))
29.         {
30.             Debug.LogError("Gc");
31.             GC.Collect();
32.         }
33.     }
34. }
35.  

 

When I did the test, GC.Collect() was called far more than six times, but the memory could not fall. And when I allocate 300m again, the memory will go up. I checked through the Memory Profiler, and there are indeed several 300m pieces of memory, and I can't find a reference to it. So how should I solve it in this case, because our json data is created by the user, I can't control its size, so it is easy to generate large memory allocation during deserialization.