Subject: "resident" executables, a COW and shared library like feature
To: None <>
From: Matthew Mondor <>
List: tech-kern
Date: 09/26/2002 02:50:47

Would anyone know if someone already implemented kernel-residentiable
executables on unix, which may share the same text area in physical memory
when many copies are being started?

I know that there are COW pages, which permit to produce similar results
when a process forks multiple times, and shared libraries which allow alot
of code to be shared among processes using it;

This however probably would look more in the form of a virtual fs
or the like, where all executables started via execve(2) would actually
share the same pages, it could also be static executables... basically it
would be similar to if the process had already been launched once, but was
sleeping in an invisible state, and a fork(2)-like operation would be
performed on it when it then gets invoked...

I mostly wonder if this already exists, or if some work was in progress
to allow such a feature, which would probably be quite useful for some
configurations, an example which comes to mind are external CGIs which an
HTTP server would start many copies at once for instance. Although this
last problem has various solutions in the web server area, this would
consists of a generic solution for other similar issues, /bin/sh itself
often has so many instances running is another example. The requirements
of vm space would be reduced, while new process setup could also be

An operating system using a similar approach was AmigaOS 2.04+, although
it required executables to be "pure", reentrant that is, and the rest
seemed to be handled with special shell support. Of course the design
was fairly different than what would have to be done on BSD