That would have to be all allocations in all processes (and the kernel and drivers)

In extreme circumstances, the OOM killer can decide to kill your process even if it barely uses any memory (a simple way to get there is by fork-bombing copies of such processes)

Also, using oom_score_adj (https://www.baeldung.com/linux/memory-overcommitment-oom-kil...) is a lot easier.