The other place it comes up is launchers and resource managers. We actually have a series of old issues and implementation work on flux (large scale resource manager for clusters) working around fork becoming a significant bottleneck in parallel launch. IIRC it showed up when we had ~1gb of memory in use and needed to spawn between 64 and 192 processes per node. That said, we actually didn’t pivot to vfork, we pivoted to posix_spawn for all but the case where we have to change working directory (had to support old glibc without the attr for that in spawn). If you’re interested I think we did some benchmarking with public results I could dredge up.
Anyway, much as I have cases where it matters I guess what I’m saying is I think you’re right that vfork is rarely actually necessary, especially since you’d probably have a much easier time getting a faster and still deterministic spawn if it ever actually becomes a bottleneck for something you care about.
> That said, we actually didn’t pivot to vfork, we pivoted to posix_spawn for all but the case where we have to change working directory (had to support old glibc without the attr for that in spawn).
You can always accomplish that sort of thing by using a helper program that ultimately execs the desired one -- just prefix it and its arguments to the intended argv.
Quite so. We would have too, but I left out the nasty bit that someone had at one point put a callback argument in an internal launching API that runs between fork and exec. Still working on squashing the last of those.
Anyway, much as I have cases where it matters I guess what I’m saying is I think you’re right that vfork is rarely actually necessary, especially since you’d probably have a much easier time getting a faster and still deterministic spawn if it ever actually becomes a bottleneck for something you care about.