[dalias]

No, fork is only one path that can lead to overcommit. Allocation of new memory as COW references to a zero page, and COW writable MAP_PRIVATE mappings of files (such as the writable LOAD segments of any executable or library file) also lead to overcommit unless you do proper commit accounting. Any system that does not need to do detailed commit accounting to avoid overcommit is basically wasting the fact that it has virtual memory/MMU.

[Sir_Cmpwn]

I never meant to suggest that fork is the only path that leads to overcommitment, but that fork/exec generally insists on overcommitment for reasonable use.