Trying to measure coreclr gc pauses under extreme pressure

Program.cs

using System;
using System.Threading;
using System.Diagnostics;
using System.Collections.Generic;

namespace hello_memory
{
    class MyObject
    {
        public int value;

        public MyObject(int value)
        {
            this.value = value;
        }
    }

    class Program
    {
        static void WatchPauses()
        {
            long[] buffer = new long[10000];
            double msPerTick = 1000.0 / Stopwatch.Frequency;
            long minTicks = Stopwatch.Frequency / 10000; // 0.1ms
            for (;;)
            {
                long lastTimestamp = Stopwatch.GetTimestamp();
                for (int i = 0; i < buffer.Length; ++i)
                {
                    long ts;
                    do
                    {
                        ts = Stopwatch.GetTimestamp();
                    } while (ts - lastTimestamp < minTicks);
                    buffer[i] = ts - lastTimestamp;
                    lastTimestamp = ts;
                }
                Array.Sort(buffer);
                Console.WriteLine("Pauses: min={0}ms p50={1}ms p99={2}ms p99.9={3}ms max={4}ms",
                    (buffer[0] - minTicks) * msPerTick,
                    (buffer[5000-1] - minTicks) * msPerTick,
                    (buffer[9900-1] - minTicks) * msPerTick,
                    (buffer[9990-1] - minTicks) * msPerTick,
                    (buffer[10000-1] - minTicks) * msPerTick);
            }
        }

        public static bool DoAllocations = true;
        public static bool DoInnerSleep = false;
        public static IList<MyObject> L;

        static void Main(string[] args)
        {
            var thread = new Thread(WatchPauses);
            thread.IsBackground = true;
            thread.Start();

            if (DoAllocations)
            {
                L = new List<MyObject>();
                for (int i = 0; i < 100_000_000; ++i)
                {
                    if (DoInnerSleep && i % 10000 == 0)
                    {
                        Thread.Sleep(1);
                    }
                    L.Add(new MyObject(i));
                }
                int sum = 0;
                for (int i = 0; i < 100_000_000; ++i)
                {
                    sum += L[i].value;
                }
                Console.WriteLine("All done! {0} items total, sum = {1}", L.Count, sum);
                Thread.Sleep(1000);

                Console.WriteLine("Memory before gc = {0}", GC.GetTotalMemory(false));
                GC.Collect();
                Console.WriteLine("Memory after gc = {0}", GC.GetTotalMemory(false));

                L.Clear();
                Console.WriteLine("Memory after clear = {0}", GC.GetTotalMemory(true));
                L = null;
                Console.WriteLine("Memory after free = {0}", GC.GetTotalMemory(true));
            }
            else
            {
                Thread.Sleep(10000);
            }
            Console.WriteLine("Sleeping for 5 seconds...");
            Thread.Sleep(5000);
        }
    }
}

results.txt

$ uname -mrs
Darwin 16.6.0 x86_64
$ dotnet run -c Release
Pauses: min=0ms p50=1.9E-05ms p99=3.911576ms p99.9=12.861823ms max=102.592996ms
Pauses: min=0ms p50=1.9E-05ms p99=0.016168ms p99.9=11.640945ms max=23.27792ms
Pauses: min=0ms p50=1.8E-05ms p99=0.095015ms p99.9=11.369459ms max=479.434985ms
All done! 100000000 items total, sum = 887459712
Pauses: min=0ms p50=1.8E-05ms p99=0.025847ms p99.9=10.579593ms max=27.44908ms
Memory before gc = 4010769264
Memory after gc = 3473889984
Pauses: min=0ms p50=5E-06ms p99=0.000642ms p99.9=0.028353ms max=1030.0839ms
Memory after clear = 1073881840
Memory after free = 139952
Sleeping for 5 seconds...
Pauses: min=0ms p50=5E-06ms p99=5.7E-05ms p99.9=0.014859ms max=1132.418091ms
Pauses: min=0ms p50=5E-06ms p99=5.2E-05ms p99.9=0.01256ms max=1.875761ms
Pauses: min=0ms p50=5E-06ms p99=0.000836ms p99.9=0.015358ms max=1.979399ms
Pauses: min=0ms p50=5E-06ms p99=0.000135ms p99.9=0.015897ms max=1.891292ms
Pauses: min=0ms p50=5E-06ms p99=5.9E-05ms p99.9=0.013745ms max=1.947827ms