From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Cross Message-Id: <200110312021.PAA15416@augusta.math.psu.edu> To: 9fans@cse.psu.edu Subject: Re: [9fans] Virtual memory in BSD and Plan9 In-Reply-To: <3BE038E9.6AC0BD50@null.net> References: <20011029123819.DCCD7199E4@mail.cse.psu.edu> Cc: Date: Wed, 31 Oct 2001 15:21:27 -0500 Topicbox-Message-UUID: 10f0293a-eaca-11e9-9e20-41e7f4b1d025 In article <3BE038E9.6AC0BD50@null.net> you write: >One big difference I've seen in past examples of paging systems >can be summarized as: page against everyone vs. page only against >oneself. The latter is sometimes called the "working set" model. >The former tends to make the whole system unusable when a process >lets its address space get out of control, while the latter tends >to run other processes pretty much the same under such conditions. Forsyth wrote an interesting paper years back called something along the lines of, ``Sending Unix to the Fat Farm,'' wherein he details his experience replacing various parts of the SunOS 3 kernel in an effort to simplify the overall system. Of particular interest was his replacement of the whole-system paging scheme inherited from 4BSD with one based on the working set model. Apparantly, the system performed much more gracefully under load as a result, in addition to being far simpler and more maintainable. One of the things that bothers me about the Linux and BSD camps is that they don't learn from such experiences of the past, and instead forge ahead with the status quo that they've inherited. For instance, the idea that Plan 9 would port one of the BSD paging subsystems is ridiculous for the same reason that the idea of porting the sockets subsystem is ridiculous; the system simply doesn't need it, it wouldn't mesh well with the overall architecture, and possibly better solutions exist in the literature. In this specific case, the subtle nuances that Dyson describes in the FreeBSD paging code are precisely the sort of thing that Plan 9 does to great lengths to avoid. Perhaps this could be accurately summed up as, ``what works for one group of people is not necessarily appropriate for all groups.'' - Dan C.