Date: Thu, 11 Feb 1999 00:59:21 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dyson@iquest.net Cc: tlambert@primenet.com, dg@root.com, dillon@apollo.backplane.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG Subject: Re: portability of shm, mmap, pipes and socket IPC Message-ID: <199902110059.RAA26636@usr08.primenet.com> In-Reply-To: <199902102136.QAA02545@y.dyson.net> from "John S. Dyson" at Feb 10, 99 04:36:15 pm
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> > 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
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