The "too small to fail" memory-allocation rule

Linux semantic of vfork is one of the most usable as it blocks only the thread in parent that calls it. Thus one can get rather safe and efficient alternative to fork/exec by creating a new thread, calling vfork from it, preparing the child and calling the exec. Compare that with, say, FreeBSD or Solaris that, according to the manual pages, suspends the whole parent process during the vfork call.