mention posix_spawn

Author: Vladimir Kotal

proc.tex

@@ -873,6 +873,11 @@
 \item Note that you have to use macros from the previous slide to get the
 child's return value out of the status information.
 \item \label{WAITPID} Example: \example{wait/wait.c}
+\item Creating new process with \texttt{fork} and replacing the process
+address space etc. with a new one after \texttt{exec} has been done is
+expensive and has other problems. To make kernel create new process directly
+from executable \texttt{posix\_spawn} can be used.
+Example: \example{exec/spawn.c}
 \end{itemize}
 
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