Comment by lloeki

7 years ago

> That's why any sane large service that needs to fork anything will early on start up a slave subprocess whose only job is to fork quickly when the master process needs it.

I don't think that's (entirely) true. This is more because a large service with some potent master process will have said process Do Stuff(tm) that will involve opening files, threads, signal handling, or whatever things that need to be taken care of one way or the other when forking to a worker (or whatever other child) process. It's therefore much simpler to fork a master subprocess into a child spawner earlier on, when it has yet to do anything. You significantly reduce your chances of screwing up if you have nothing to clean up for.

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lloeki

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evilotto  7 years ago

That's true, it's not the only reason. Dealing with threads and buffers and pthread_atfork and the associated heartbreak is a biggie also. But the performance is nothing to laugh at.

I just did a quick test, a 100mb process generally takes >2ms to fork, while a 1mb or less process takes 70us. It seems like its pretty much linear with process size.