I think one of the main reason overcommit is a thing on Linux (certainly one of the things one runs into if one turns it off) is dealing with the weirdness of f

I think one of the main reason overcommit is a thing on Linux (certainly one of the things one runs into if one turns it off) is dealing with the weirdness of fork()/exec(). For a moment there in between the two calls you _technically_ have double the RSS allocated - so spawning processes with fork()/exec() from a process with very large RSS is dicey if you don't want to technically overcommit the memory. Since 99.9% of the time very little of that memory is touched/COW'd before the exec() letting it overcommit rather than dying when a 4GB process tries to spawn a new child just because you don't have another spare 4GB of ram sitting around "just in case" is seen as a reasonable tradeoff. (Modulo vfork() and spawn() of course which are different and arguably better solutions to this issue.)