RedactStage will create a SimpleMemoryUsageTracker using createChunkedSimpleMemoryUsageTrackerForStage. No per-stage limit is configured so the default INT_MAX is used. At the start of doGetNext(), the input document size is added to the tracker. The tracker is threaded through RedactProcessor::process() --> Expression::evaluate() via EvaluationContext. The flags gFeatureFlagExpressionMemoryTracking and gFeatureFlagMemoryTracking must be checked before assigning the tracker to the EvaluationContext.