using System;
using System.Diagnostics;

static class Program
{
    static void Main(string[] args)
    {
        Console.WindowWidth = 120;

        long[] data = null;
        Measure("Alloc 1 mb", () =>
        {
            data = new long[1024 * 1024 / 8];
            return data.Length;
        });
        GC.KeepAlive(data);

        Measure("Alloc 1 gb", () =>
        {
            data = new long[1024 * 1024 * 1024 / 8];
            return data.Length;
        });
        GC.KeepAlive(data);

        // run as x64; set <gcAllowVeryLargeObjects> !!!
        Measure("Alloc 4 gb", () =>
        {
            data = new long[1024 * 1024 * 1024 / 2];
            return data.Length;
        });
        GC.KeepAlive(data);

        Console.WriteLine("Done.");
        Console.ReadKey();
    }


    static void Measure(string name, Func<long> callback)
    {
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();

        var mem = GC.GetTotalMemory(true);
        var gc00 = GC.CollectionCount(0);
        var gc01 = GC.CollectionCount(1);
        var gc02 = GC.CollectionCount(2);

        var sw = Stopwatch.StartNew();
        var result = callback();
        sw.Stop();

        var mem2 = GC.GetTotalMemory(false);
        var gc10 = GC.CollectionCount(0);
        var gc11 = GC.CollectionCount(1);
        var gc12 = GC.CollectionCount(2);

        var memDelta = (mem2 - mem) / 1024.0;
        var gcDelta0 = gc10 - gc00;
        var gcDelta1 = gc11 - gc01;
        var gcDelta2 = gc12 - gc02;

        Console.WriteLine(
            "{0,20}: {1,5}ms, ips: {2,22:N} | Mem: {3,9:N2} kb, GC 0/1/2: {4}/{5}/{6} => {7,6}",
            name, sw.ElapsedMilliseconds, result / sw.Elapsed.TotalSeconds, memDelta, gcDelta0, gcDelta1, gcDelta2, result);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <runtime>
        <gcAllowVeryLargeObjects enabled="true" />
    </runtime>
</configuration>

using System;
using System.Diagnostics;

static class Program
{
    private static void ForceMemAccess(ref long l)
    {
        l = 1;
    }

    static void Main(string[] args)
    {
        const int PageSize = 4096 / 2;
        Console.WindowWidth = 120;

        long[] data = null;

        for (int n = 1; n <= 8; n++)
        {
            data = null;

            var allocSize = n * 512 * (1024 * 1024 / sizeof(long));

            Measure($"Alloc {n * 0.5:N2} Gb", () =>
            {
                data = new long[allocSize];
                GC.KeepAlive(data[0]);
                return data.Length;
            });
            GC.KeepAlive(data);

            Measure("Consume1", () =>
            {
                var local = data;
                for (int i = 0; i < local.Length; i += PageSize)
                {
                    ForceMemAccess(ref local[i]);
                }
                return data.Length;
            });

            Measure("Consume2", () =>
            {
                var local = data;
                for (int i = 0; i < local.Length; i += PageSize)
                {
                    ForceMemAccess(ref local[i]);
                }
                return data.Length;
            });

            GC.KeepAlive(data);

            Console.WriteLine();
        }

        Console.WriteLine("Done.");
        Console.ReadKey();
    }


    static void Measure(string name, Func<long> callback)
    {
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();

        var mem = GC.GetTotalMemory(true);
        var gc00 = GC.CollectionCount(0);
        var gc01 = GC.CollectionCount(1);
        var gc02 = GC.CollectionCount(2);

        var sw = Stopwatch.StartNew();
        var result = callback();
        sw.Stop();

        var mem2 = GC.GetTotalMemory(false);
        var gc10 = GC.CollectionCount(0);
        var gc11 = GC.CollectionCount(1);
        var gc12 = GC.CollectionCount(2);

        var memDelta = (mem2 - mem) / 1024.0;
        var gcDelta0 = gc10 - gc00;
        var gcDelta1 = gc11 - gc01;
        var gcDelta2 = gc12 - gc02;

        Console.WriteLine(
            "{0,20}: {1,5}ms, ips: {2,22:N} | Mem: {3,12:N2} kb, GC 0/1/2: {4}/{5}/{6} => {7,6}",
            name, sw.ElapsedMilliseconds, result / sw.Elapsed.TotalSeconds, memDelta, gcDelta0, gcDelta1, gcDelta2, result);
    }
}