vi core dumping on Sun 2 (fixed, but would like explanations)

[Guy Harris]

> What we think happened (and we were never able to prove it since the problem
> never re-occurred), is that 4.2 (and 4.1, and 4.0) does not give up pages of
> pure-text programs when the program exits, but marks them as pages of
> pure-text programs in case if the program is run again soon, then the page
> does not have to be read in again from disk.

This is, indeed the case.  (Try bringing up a 4.xBSD machine up single-user,
timing a compile, and then timing the same compile.  The second one will be
faster, both due to the pagein of the compiler passes being bypassed and due
to the inode for the passes and input files (and their directory entries, in
4.3BSD) being in an in-core cache.  Of course, if you have so little
physical memory that each pass of the compiler flushes the previous one out
of memory, you won't get any speedup; the blocks won't be in the buffer
cache because pageins don't go through the buffer cache.)

	Guy Harris