I've left it running for over a week, and the memory use gets to be Quite Big:
VIRT RES SHR S %CPU %MEM TIME+ COMMAND
23.0g 18.3g 17.9g R 162.3 58.4 35322:54 NQL.x86_64
Memory used + reserved - 23.0 GiB
Non-swapped actual physical memory used - 18.3 GiB
Most (17.9 GiB) of that is shared.. but it's still taking up over half of the RAM here, and these are way higher figures than at the start of running it.
I wondered if it was the log file being held in RAM, but that's 'only' 603 MB.