Between two consecutive iterations, compaction may not save much space but still evaluates the table as compactable. If the amount of saved space is below a specific threshold or if it is evaluated as not worth the potential disruption caused by compaction after N iterations, we should quit. Currently, the maximum number of iterations is set to 100. We have seen cases in SERVER-80124 where 25 iterations take 1h and no space is actually being reclaimed.