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From: "John S. Dyson" <toor@dyson.iquest.net>
Message-Id: <199612100238.VAA27569@dyson.iquest.net>
Subject: Re: Multiple Buffer allocation of Shared Memory
To: erich@lodgenet.com (Eric L. Hernes)
Date: Mon, 9 Dec 1996 21:38:50 -0500 (EST)
Cc: scrappy@hub.org, hackers@FreeBSD.ORG
In-Reply-To: <199612100156.TAA00658@jake.lodgenet.com> from "Eric L. Hernes" at Dec 9, 96 07:56:17 pm
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> 
> Shared memory is cool, SysV symantics for shared memory *suck*, if at all
> possible use mmap(). BSDi uses libc wrappers around mmap() for
> it's SysV shm stuff, but there's caveats... I'd like the wrappers,
> but have the real ones available too.
> 
FreeBSD, NetBSD, and OpenBSD have a low level implementation of the
SYSVSHM stuff (not based on mmap, but on some of the low level kernel primatives
that are also used to implement mmap.)

> 
> you can only have 8 shm segments by default, you can override
> it with: `options "SHMSEG=32"' or something similar in your config file.
> I usually bump SHMSEG to 128 and SHMMAXPGS to 4096.
> 
The limits on FreeBSD are totally administrative, and so if you need to
increase SHMMAXPGS or somesuch, there is little cost.

John
dyson@freebsd.org