alt Hacker News> […] because after the fork writes to basically any page in either process will trigger memory commitment.
This is largely not true for most processes. For a child process to start writing into its own data pages en masse, there has to exist a specific code path that causes such behaviour. Processes do not randomly modify their own data space – it is either a bug or a peculiar workload that causes it.
You would have a stronger case if you mentioned, e.g., the JVM, which has a high complexity garbage collector (rather, multiple types of garbage collectors – each with its own behaviour), but the JVM ameliorates the problem by attempting to lock in the entire heap size at startup or bailing if it fails to do so.
In most scenarios, forking a process has a negligible effect on the overall memory consumption in the system.
> This is largely not true for most processes.
> In most scenarios, forking a process has a negligible effect on the overall memory consumption in the system.
Yes, that’s what they’re getting at. It’s good overcommitment. It’s still overcommitment, because the OS has no way of knowing whether the process has the kind of rare path you’re talking about for the purposes of memory accounting. They said that disabling overcommit is wasteful, not that fork is wasteful.