Re: [9fans] Virtual memory in BSD and Plan9

[Dan Cross <cross@math.psu.edu>]

In article <3BE038E9.6AC0BD50@null.net> you write:
>One big difference I've seen in past examples of paging systems
>can be summarized as: page against everyone vs. page only against
>oneself.  The latter is sometimes called the "working set" model.
>The former tends to make the whole system unusable when a process
>lets its address space get out of control, while the latter tends
>to run other processes pretty much the same under such conditions.

Forsyth wrote an interesting paper years back called something along
the lines of, ``Sending Unix to the Fat Farm,''  wherein he details his
experience replacing various parts of the SunOS 3 kernel in an effort
to simplify the overall system.

Of particular interest was his replacement of the whole-system paging
scheme inherited from 4BSD with one based on the working set model.
Apparantly, the system performed much more gracefully under load as a
result, in addition to being far simpler and more maintainable.

One of the things that bothers me about the Linux and BSD camps is that
they don't learn from such experiences of the past, and instead forge
ahead with the status quo that they've inherited.  For instance, the
idea that Plan 9 would port one of the BSD paging subsystems is
ridiculous for the same reason that the idea of porting the sockets
subsystem is ridiculous; the system simply doesn't need it, it wouldn't
mesh well with the overall architecture, and possibly better solutions
exist in the literature.  In this specific case, the subtle nuances
that Dyson describes in the FreeBSD paging code are precisely the sort
of thing that Plan 9 does to great lengths to avoid.

Perhaps this could be accurately summed up as, ``what works for one
group of people is not necessarily appropriate for all groups.''


	- Dan C.