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From: friesen@psivax.UUCP (Stanley Friesen)
Newsgroups: net.arch
Subject: Re: Large Main Memories
Message-ID: <1426@psivax.UUCP>
Date: Wed, 10-Sep-86 13:52:07 EDT
Article-I.D.: psivax.1426
Posted: Wed Sep 10 13:52:07 1986
Date-Received: Fri, 12-Sep-86 07:03:38 EDT
References: <1161@bu-cs.bu-cs.BU.EDU> <2065@sdcsvax.UUCP>
Reply-To: friesen@psivax.UUCP (Stanley Friesen)
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 20

In article <2065@sdcsvax.UUCP> hutch@sdcsvax.UUCP (Jim Hutchison) writes:
 
>Zeroing of pages need not be done all at once.
>Right now, if you have extra memory lying about (unusual yes, but read on),
>it does not get 0'd until somebody grabs a "blank" page.  How about a mode
>like "0 on reference"?  There is "copy on write" in some places, why not?
>Then you only have to worry about 1 page at a time.  Extra swap space is not
>costing you anything, why should extra memory?  Huh?

	As a matter of fact demand-paged UNIX's(Sys Vr2+ & BSD 4.x) do exactly
that! They call them zero-fill pages. It is implemented using page
table entries with the valid bit off and a software flag marking the
entry a zero-fill page. On a page fault from such a page the kernal
allocates a free page frame and zeros it.
---

				Sarima (Stanley Friesen)

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