From owner-freebsd-hackers Wed Feb 10 18:21:06 1999 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id SAA01677 for freebsd-hackers-outgoing; Wed, 10 Feb 1999 18:21:06 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from smtp04.primenet.com (smtp04.primenet.com [206.165.6.134]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id SAA01646 for ; Wed, 10 Feb 1999 18:21:00 -0800 (PST) (envelope-from tlambert@usr06.primenet.com) Received: (from daemon@localhost) by smtp04.primenet.com (8.8.8/8.8.8) id TAA10064; Wed, 10 Feb 1999 19:24:13 -0700 (MST) Received: from usr06.primenet.com(206.165.6.206) via SMTP by smtp04.primenet.com, id smtpd009740; Wed Feb 10 19:23:59 1999 Received: (from tlambert@localhost) by usr06.primenet.com (8.8.5/8.8.5) id TAA08932; Wed, 10 Feb 1999 19:20:17 -0700 (MST) From: Terry Lambert Message-Id: <199902110220.TAA08932@usr06.primenet.com> Subject: Re: portability of shm, mmap, pipes and socket IPC To: dillon@apollo.backplane.com (Matthew Dillon) Date: Thu, 11 Feb 1999 02:20:14 +0000 (GMT) Cc: tlambert@primenet.com, dyson@iquest.net, dg@root.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG In-Reply-To: <199902110119.RAA87393@apollo.backplane.com> from "Matthew Dillon" at Feb 10, 99 05:19:34 pm X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > :> The condition for paging out pages to SysV SHM are very similar to anonymous > :> MMAPed regions. There is no effective difference. If you use file backed > :> MMAPed regions, there are some time consuming sync operations though. > : > :The difference is that anonymous MMAPed regions can only be mapped > :into multiple processes via forke based inheritance. > : > :This makes them useless for sotheming that, for example, attaches to > :a shared context segment shared by several processes acting as > :work-to-do engines, so as to be able to examine and manipulate the > :shared idea of the current context contents. > : > :This limitation is the specific reason that NetWare for UNIX uses shared > :memory segments instead of mmap'ed regions for client context records. > > ... and has absolutely nothing to do with the question that John was > replying to, which was related to the fault overhead/expense of using > mmap() verses a SYS-V shared memory segment. But has everything to do with his statement to the effect that "There is no effective difference", contained in the answer. The rest was quoted for context. I am not so stupid that I cannot fathom his answer, as you would see if you read the rest of the messages in this thread, where I said "Mea culpa" ("My Fault") to David's quotation of John's reply in a different context. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message