BSD virtual memory mngmt algorithm. Was: Performance Tuning Ultrix 4.1

[Chris Torek]

In article <16121 at smoke.brl.mil> gwyn at smoke.brl.mil (Doug Gwyn) writes:
>Other than Sun, almost all ports of 4.nBSD have had to overhaul the
>virtual memory code, which was written quite narrowly for a VAX-like
>VM system.  (Sun simply BUILT a VAX-like VM system!)

Well no: while the old VM was rather icky and somewhat painful to
modify for 3-level schemes such as the i386 and 68030, it did work
pretty well for anything that had hardware PTEs.

Sun did not build a VAX-like VM system, if by `system' you mean `MMU';
the Sun MMU is much more like a TLB.  What they did, rather, was make
software PTEs that simulated a VAX.

The current BSD development systems have a Mach-based VM (with a few,
ah, `interesting' bugs) which is scheduled to change rather a lot over
the next few months....
-- 
In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE (+1 415 486 5427)
Berkeley, CA		Domain:	torek at ee.lbl.gov