Date: Wed, 10 Feb 1999 17:19:34 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Terry Lambert <tlambert@primenet.com> Cc: dyson@iquest.net, tlambert@primenet.com, dg@root.com, kuku@gilberto.physik.RWTH-Aachen.DE, hackers@FreeBSD.ORG Subject: Re: portability of shm, mmap, pipes and socket IPC Message-ID: <199902110119.RAA87393@apollo.backplane.com> References: <199902110059.RAA26636@usr08.primenet.com>
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:> > 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
... 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.
-Matt
Matthew Dillon
<dillon@backplane.com>
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