The biggest reason overcommit exists is because it allows the system to operate more efficiently. The reality is most applications touch only some of the pages they allocate, and it's silly for the system to fail a malloc. Often times other expensive cleanup activities can be deferred (you don't really want to drop a handy directory entry cache just so an app can be sure it got physically backed memory for its request, 99.99% of the time).
IIUC Linux was really the first OS to make overcommit so prominent. Most systems were a lot more conservative.
IIUC Linux was really the first OS to make overcommit so prominent. Most systems were a lot more conservative.