Date: Thu, 11 Feb 1999 02:20:14 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: tlambert@primenet.com, dyson@iquest.net, dg@root.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG Subject: Re: portability of shm, mmap, pipes and socket IPC Message-ID: <199902110220.TAA08932@usr06.primenet.com> In-Reply-To: <199902110119.RAA87393@apollo.backplane.com> from "Matthew Dillon" at Feb 10, 99 05:19:34 pm
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> :> 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.
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