The Linux kernel has a feature where you can tune the behavior of memory allocations: the vm.overcommit_memory sysctl. When overcommit is enabled (sadly, this is the default), the kernel will typically return a mapping when brk(2) or mmap(2) is called to increase a program’s heap size, regardless of whether or not memory is available. Sounds good, right? Not really. While overcommit is convenient for application developers, it fundamentally changes the contract of memory allocation: a successful allocation no longer represents an atomic acquisition of a real resource.