NodeMemoryExpression.java

...
childImplementations.put(FREE, new MemoryExpression(FREE) {
    @Override
    public Long value() {
        return osService.stats().mem().actualFree().bytes();
    }
});
childImplementations.put(USED, new MemoryExpression(USED) {
    @Override
    public Long value() {
        return osService.stats().mem().actualUsed().bytes();
    }
});
childImplementations.put(FREE_PERCENT, new MemoryExpression(FREE_PERCENT) {
    @Override
    public Short value() {
        return osService.stats().mem().freePercent();
    }
});
childImplementations.put(USED_PERCENT, new MemoryExpression(USED_PERCENT) {
    @Override
    public Short value() {
        return osService.stats().mem().usedPercent();
    }
});
...