I forgot the exact number, but I remember reading somewhere that for a garbage collector to work well you need to give it something like 3 or 4 times more space

I forgot the exact number, but I remember reading somewhere that for a garbage collector to work well you need to give it something like 3 or 4 times more space than you will actually be using at maximum allocation - not counting transient stuff. This allows it to shuffle things around more effectively while it is cleaning up, doing things like copying into a compacted area.