vfork

[johnl at ima.UUCP]

/* Written  1:22 am  Jul  8, 1985 by thomas at utah-gr in ima:net.unix-wizards */
> The problem is that the initial design of the Vax (750?) had a flaw that
> made copy-on-write VERY difficult (impossible?) to do.  So, the vfork
> kludge was the only workable solution to avoid copying an entire process

No it wasn't -- vfork really has to be chalked up to laziness.  It would
have been entirely workable to do copy-on-touch in the stack segment (which
was where the copy-on-write pages didn't work.)  Considering how little
stack data is read but not written, the performance would have been about
the same.

On machines like the PDP-11, vfork makes more sense since the segments
are too big to do practical copy-on-anything.

John Levine, ima!johnl