presto-main/src/main/java/io/prestosql/operator/HashAggregationOperator.java/HashAggregationOperator/startMemoryRevoke
class HashAggregationOperator:    @Override
    public ListenableFuture<?> startMemoryRevoke()
    {
        if (aggregationBuilder != null) {
            return aggregationBuilder.startMemoryRevoke();
        }
        return NOT_BLOCKED;
    }