Simplest example is to allocate and pin all your resources on startup. If it crashes, it does so immediately and with a clear error message, so the solution is as straightforward as "pass bigger number to --memory flag" or "spec out larger machine".
Overcommit means that the act of memory allocation will not report failure, even when the system is out of memory.
Instead, failure will come at an arbitrary point later, when the program actually attempts to use the aforementioned memory that the system falsely claimed had been allocated.
Allocating all at once on startup doesn't help, because the program can still fail later when it tries to actually access that memory.
Or, even simpler, just turn off over-commit.
But if swap comes into the mix, or just if the OS decides it needs the memory later for something critical, you can still get killed.
(I understand that mlock prevents paging-out, but in my mind that's a separate concern from pre-faulting?)