Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.arch Subject: Re: Page size and the meaning of life Message-ID: <6085@utzoo.UUCP> Date: Sat, 26-Oct-85 21:16:36 EDT Article-I.D.: utzoo.6085 Posted: Sat Oct 26 21:16:36 1985 Date-Received: Sat, 26-Oct-85 21:16:36 EDT References: <926@decwrl.UUCP> <931@lll-crg.ARpA> <7459@watdaisy.UUCP>, <939@lll-crg.ARpA> Organization: U of Toronto Zoology Lines: 19 > ... The much needed firewall protection and address space shareing > for programs in a multiprocessor can be provided by a simple {base,limit} > segmentation scheme. One or course needs several sets of such registers... There are a couple of very useful tricks one can pull with paged systems that cannot be done with base-limit schemes. For one thing, it is possible to enlarge a process's stack without having to move the whole thing around in memory (scatter allocation). For another, it is possible to do a much more efficient implementation of fork() using copy-on-write techniques. Neither of these matters too much for small processes, but they start to be major considerations for really big ones. Note that it is possible to overlap page-translation time with memory- access time, as on the Celerity C1200, so that very little speed penalty is incurred. Generalizing this to supercomputers with 50-ns memory is not so straightforward, admittedly. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry