Path: utzoo!utgpu!water!watmath!clyde!att-cb!att-ih!alberta!ncc!uunet!husc6!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!sequent!rbk
From: rbk@sequent.UUCP (Bob Beck)
Newsgroups: comp.unix.wizards
Subject: Re: Shared Memory in BSD4.3 is lacking?
Message-ID: <3255@sequent.UUCP>
Date: 8 Mar 88 01:28:50 GMT
References: <12137@brl-adm.ARPA>
Reply-To: rbk@crg2.UUCP (Bob Beck)
Organization: Sequent Computer Systems, Beaverton, OR
Lines: 18

In article <12137@brl-adm.ARPA> rbj@icst-cmr.arpa (Root Boy Jim) writes:
>
>Your friends at Sequent do the same thing. However, what they are
>really doing is marking certain pieces of the buffer cache resident
>and non-reclaimable, then mapping them into the processes space.

Not true.  mmap() works in Dynix by mapping portions of files into address
spaces on page boundaries.  The file acts as a paging source and store for
the data; the pages of the file are demand loaded directly into user
addressible memory, no buffer cache involved.  The buffer cache does remain
coherent, however, so read/write system calls see the latest data.

					Bob Beck
					Sequent Computer Systems
					15450 SW Koll Parkway
					Beaverton, Oregon  97006
					...{tektronix,ogcvax}!sequent!rbk
					(503)626-5700