From owner-freebsd-hackers Wed Feb 10 16:59:38 1999 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id QAA21692 for freebsd-hackers-outgoing; Wed, 10 Feb 1999 16:59:38 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from smtp01.primenet.com (smtp01.primenet.com [206.165.6.131]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id QAA21682 for ; Wed, 10 Feb 1999 16:59:34 -0800 (PST) (envelope-from tlambert@usr08.primenet.com) Received: (from daemon@localhost) by smtp01.primenet.com (8.8.8/8.8.8) id RAA06755; Wed, 10 Feb 1999 17:59:31 -0700 (MST) Received: from usr08.primenet.com(206.165.6.208) via SMTP by smtp01.primenet.com, id smtpd006728; Wed Feb 10 17:59:23 1999 Received: (from tlambert@localhost) by usr08.primenet.com (8.8.5/8.8.5) id RAA26636; Wed, 10 Feb 1999 17:59:21 -0700 (MST) From: Terry Lambert Message-Id: <199902110059.RAA26636@usr08.primenet.com> Subject: Re: portability of shm, mmap, pipes and socket IPC To: dyson@iquest.net Date: Thu, 11 Feb 1999 00:59:21 +0000 (GMT) Cc: tlambert@primenet.com, dg@root.com, dillon@apollo.backplane.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG In-Reply-To: <199902102136.QAA02545@y.dyson.net> from "John S. Dyson" at Feb 10, 99 04:36:15 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 > > I guess if we are still examining Linux vs. FreeBSD programming, then > > I should probably point out that SysV SHM is faster than non-anonymous > > mmap'ed memory, because writes don't have to be written through to the > > backing object. > > 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. 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