swap space

[Rob Healey]

In article <1991Jun15.195720.25820 at cs.UAlberta.CA> adam at cs.UAlberta.CA (Michel Adam;  Gov't of NWT) writes:
=I seem to remember a discussion on this subject, 6 to 12 months ago, on the
=problems with insufficient RAM available on the AT&T 386 machines, (must have
=been a SYS V Ver. 3.something). One comment that struck my mind at that time
=was that for some reason, there was a recommendation to have as much real RAM
=as the swap partition's size ( I may be mistaken on that ...), to avoid some
=kind of trashing. There was an explicit reference to the implementation
=by Convergent, for the 7300, being somewhat different and managing to avoid
=this problem. There where numerous references to the Bach book, but I don't
=remember if the difference between the CT version for the 3B1 and the other
=versions running on 386 machine was described.
=
=Can someone who archived these articles look up the conclusion? What was it
=that CT did differently in their implementation?
=
	They used a better processor family... B^). They also grafted 4.1BSD
	VM onto a System V R2 kernel. As such, you HAVE to have enough
	swap to page in the whole program to swap and then memory. I.e. I
	ran into troubles on a UNIX PC where I had 700k free memory but
	only 100k of swap, the system REFUSED to load a 400k program; sucked
	rocks. This just goes to show that both methods have their "evil twin"
	side. SVR3.x chews up too much swap, Early BSD needs enough swap for the
	whole initial program even if there is enough main memory but not
	enough swap/paging.

	I believe SVR4 and 4.3 BSD are better at paging and are more
	reasonable with it all. If nothing else you can add paging files
	under both to solve the running out of swap problem, you just take
	performance hits when the paging file blocks are scattered all
	over a disk.

		-Rob