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Date:      Thu, 5 Dec 2002 18:48:39 -0800
From:      David Schultz <dschultz@uclink.Berkeley.EDU>
To:        Gary Thorpe <gathorpe79@yahoo.com>
Cc:        Terry Lambert <tlambert2@mindspring.com>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: maxusers and random system freezes
Message-ID:  <20021206024839.GA14624@HAL9000.homeunix.com>
In-Reply-To: <20021205194604.79160.qmail@web41207.mail.yahoo.com>
References:  <3DEEB45A.BEDF8EA5@mindspring.com> <20021205194604.79160.qmail@web41207.mail.yahoo.com>

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Thus spake Gary Thorpe <gathorpe79@yahoo.com>:
> As far as I know, Linux maps all the memory in the machine into the
> kernel address space, so there is never a problem of it running out
> while there is free memory (if you run out of it, there isn't any at
> all left in the machine). It also permits the kernel to directly modify
> processes' address spaces???

Linux used to do that, but AFAIK it doesn't anymore.  Mapping all
of physical memory into KVA simplifies copyin() and copyout(), but
it restricts the amount of usable physical memory to well under
4GB.  They couldn't possibly have kept doing things this way when
they added support for all of the bank switching crap on i386.

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