Path: utzoo!attcan!uunet!dev!dgis!jkrueger From: jkrueger@dgis.dtic.dla.mil (Jon) Newsgroups: comp.arch Subject: Re: Paging page tables Message-ID: <920@dgis.dtic.dla.mil> Date: 9 Jul 90 18:55:08 GMT References: <3300142@m.cs.uiuc.edu> <9758@pt.cs.cmu.edu> <58001@bbn.BBN.COM> <5796@titcce.cc.titech.ac.jp> <1990Jul6.160004.896@zoo.toronto.edu> <5813@titcce.cc.titech.ac.jp> Organization: Defense Technical Information Center (DTIC), Alexandria VA Lines: 27 mohta@necom830.cc.titech.ac.jp (Masataka Ohta) writes: >With copy-on-write scheme, a page need swap space >when the page is written something. But not until. Page and swap file space allocation is as postponeable as the memory copy. Again, the cost is not paid at process creation and quite commonly not ever. In UNIX systems the most common sequence of events after a fork is an exec. Why allocate swap space at process creation when the most common immediately following event will be execution of a different sized program? >If you think virtual memory is free and allow forking without reserving >actual swap space, when swap space is required, it is often the case >that, there is no free swap space, anymore. That way lies MVS, friends; can't do anything without allocating all resources you might ever use, paying for them whether you ever use them or not, denying them to others, including your own other processes. If you want MVS you know where to find it. The rest of us have found more flexible resource management schemes worthwhile. We love ownership but also find option-to-buy an attractive proposition. -- Jon -- Jonathan Krueger jkrueger@dtic.dla.mil uunet!dgis!jkrueger Drop in next time you're in the tri-planet area!