That's referred to as rubber hose cryptography.
It's based on the game theoretic idea that if your adversary has no way of knowing how many hidden partitions you have, then you have no way of proving to them that you've given them all your secrets.
As such, there is no benefit to you revealing any secrets under torture, because the torture would continue even after you've told them everything, therefore there is no point to them torturing you in the first place.
[0] https://en.wikipedia.org/wiki/Rubberhose_%28file_system%29
In reality they will torture you until you stop decrypting partitions, and then a bit more of special torture, just in case.
If a torturer has good reason to believe you have valuable information regarding subject X, they'll simply torture you until they possess that information or you die. If you don't possess the information, you're screwed. If you do possess the information, it's likely that they'll stop after they get what they're after.
If you're in the business of protecting your secrets against torture then you need to also be protecting them against death because that is grimly inevitable.