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From: torek@elf.ee.lbl.gov (Chris Torek)
Newsgroups: comp.unix.wizards
Subject: Re: BSD virtual memory mngmt algorithm. Was: Performance Tuning Ultrix 4.1
Keywords: paging swapping fast large load BSD
Message-ID: <13087@dog.ee.lbl.gov>
Date: 11 May 91 12:53:55 GMT
References: <1991Apr30.160331.16215@milton.u.washington.edu> <1991May7.065338.1027@ubeaut.enet.dec.com> <16121@smoke.brl.mil>
Reply-To: torek@elf.ee.lbl.gov (Chris Torek)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 19
X-Local-Date: Sat, 11 May 91 05:53:55 PDT

In article <16121@smoke.brl.mil> gwyn@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@ee.lbl.gov