OnGcHeapStats.cs

// This event provides the size of each generation after the collection
// Note: last event for non background GC (will be GCGlobalHeapHistory for background gen 2)
private void OnGcHeapStats(EventWrittenEventArgs e)
{
    var currentGC = GetCurrentGC(_gcInfo);
    if (currentGC == null)
        return;

    currentGC.Heaps.Gen0Size = (long)GetFieldValue<ulong>(e, "GenerationSize0");
    currentGC.Heaps.Gen1Size = (long)GetFieldValue<ulong>(e, "GenerationSize1");
    currentGC.Heaps.Gen2Size = (long)GetFieldValue<ulong>(e, "GenerationSize2");
    currentGC.Heaps.LOHSize = (long)GetFieldValue<ulong>(e, "GenerationSize3");

    // this is the last event for non background collections  during a background gen2 collections
    if (
        (_gcInfo.CurrentBGC != null) &&
        (currentGC.Generation < 2)
       )
    {
        GcEvents?.Invoke(this, BuildGcArgs(currentGC));
        _gcInfo.GCInProgress = null;
    }
}