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Date:      Thu, 11 Feb 1999 03:23:07 -0500 (EST)
From:      "John S. Dyson" <dyson@iquest.net>
To:        mike@smith.net.au (Mike Smith)
Cc:        dyson@iquest.net, dg@root.com, tlambert@primenet.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:  <199902110823.DAA03550@y.dyson.net>
In-Reply-To: <199902102350.PAA01211@dingo.cdrom.com> from Mike Smith at "Feb 10, 99 03:50:51 pm"

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Mike Smith said:
> > David Greenman said:
> > > >> >:The overall size of the shared memory segment is limited to that
> > > >> >:	which can fit in the kernels virtual address space; this
> > > >> >:	artificially restricts the maximum size.
> > > >> 
> > > >>    That isn't true and hasn't been true for several years in FreeBSD.
> > > >
> > > >Are you sure?
> > > 
> > >    Yes, I'm quite sure.
> > > 
> > DG's statement is accurate.  I removed that very artificial restriction over
> > 2 yrs ago.  There is no reason to use KVA space for data that the kernel never
> > needs to see.  Correcting that deficit was pretty much on my list as soon as
> > I saw that problem when FreeBSD made it an official part of the distribution.
> 
> Hmm, so does that mean that the shared memory pages can be paged out?  
> And if so, should we be removing the SHMMAXPGS kernel option (since our 
> current shared memory profile is woefully inadequate for most uses)?
> 
Shared memory pages *can* be paged out.  There are policy issues that DG
and others (maybe including you) need to evaluate before deciding that
SHMMAXPGS isn't something that is desirable.  I suspect that SHMMAXPGS is
pretty much redundant, but... :-).

-- 
John                  | Never try to teach a pig to sing,
dyson@iquest.net      | it makes one look stupid
jdyson@nc.com         | and it irritates the pig.

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