Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!src.honeywell.com!msi.umn.edu!noc.MR.NET!nic.stolaf.edu!thor.acc.stolaf.edu!mike From: mike@thor.acc.stolaf.edu (Mike Haertel) Newsgroups: comp.arch Subject: Re: Sun bogosities, including MMU thrashing Message-ID: <1991Jan22.174444.12312@acc.stolaf.edu> Date: 22 Jan 91 17:44:44 GMT References: <5257@auspex.auspex.com> <3956@skye.ed.ac.uk> <5390@auspex.auspex.com> <1991Jan21.225211.17757@gpu.utcs.utoronto.ca> Sender: news@acc.stolaf.edu Reply-To: mike@thor.acc.stolaf.edu () Organization: St. Olaf College; Northfield, MN Lines: 32 In article <1991Jan21.225211.17757@gpu.utcs.utoronto.ca> dennis@gpu.utcs.utoronto.ca (Dennis Ferguson) writes: >While I'm unwilling to dig through the references to determine whether >Thompson and Ritchie actually said this, if they did I do think they may >have changed their minds about it. The file system used (on Vaxes) by >Version 8 was essentially the V7 file system with the block size increased >to 4096. If memory serves, the stated reason this was done was simply >that it made the file system run 8 times faster under typical loads. >And I distinctly remember arguments being made at the time to the effect >that the speed of the Berkeley fast file system (still a fairly recent >innovation then) was almost exclusively due to the larger block size, and >that the block clustering algorithm, which makes the supporting code complex >and relatively CPU-intensive when writing, really was unnecessary. My ninth edition manual documents 2 types of file systems: 1. a version-7 style file system with the block size increased to 1K. 2. a bitmapped file system with 4K blocks. I suspect that increasing the block size of a v7 file system from 1K to 4K does not give nearly as dramatic a performance improvement as going to a bit mapped free list with a localized allocation policy. The bit map for the 4K v9 file system is held entirely in the super block, in an array of 961 longs, and hence the file system cannot be larger than 961*32*4096 == ~125 MB. Note that this does not necessarily contradict your post: It's possible that v8 had a 4K v7-style file system, and that the bit mapped file system did not appear until later, but I don't have a v8 manual and so can't check. -- Mike Haertel "He's a tie with the ambition to become a full-blown suit." -- Jon Westbrock