Path: utzoo!attcan!uunet!samsung!think!barmar
From: barmar@think.com (Barry Margolin)
Newsgroups: comp.arch
Subject: Re: Tradeoffs
Message-ID: <37308@think.Think.COM>
Date: 9 Jun 90 18:09:03 GMT
References: <136844@sun.Eng.Sun.COM>
Sender: news@Think.COM
Reply-To: barmar@think.com (Barry Margolin)
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 26


In article <136844@sun.Eng.Sun.COM>, Marty Itzkowitz writes:
>The main argument for NOT letting the virtual memory system deal with it
>is that the program has a much better idea of an appropriate strategy
>for page replacement than the OS can infer from past behavior.  When the
>user switches to a new file the editor can infer that the pages from the
>previous edit can be discarded, whereas the OS will assume that if
>they were recently used they ought to be kept.

I sure hope no one adds this "feature" to my Emacs.  I frequently jump back
and forth between two or three editor buffers.  Flushing the previous
buffer from memory would pessimize this.

All that LRU assumes that if they are more recently used than some other
page then they should be kept in preference to that other page.  Can you
think of something that is likely to have been used less recently than the
pages from the current and previous buffers but that is more likely to be
used soon after switching to the current buffer?

It is certainly true that there are applications where LRU is not a good
page replacement algorithm, but I don't think this is one of them.
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar