From: Oliver Neukum <oliver@neukum.org>
To: Josh Boyer <jdub@us.ibm.com>
Subject: Re: Why does the kernel need a gig of VM?
Date: Fri, 28 Jan 2005 22:42:58 +0100
User-Agent: KMail/1.7.1
Cc: John Richard Moser <nigelenki@comcast.net>, linux-kernel@vger.kernel.org
References: <41FA9B37.1020100@comcast.net> <1106944969.7542.13.camel@windu.rchland.ibm.com>
In-Reply-To: <1106944969.7542.13.camel@windu.rchland.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-2"
Content-Transfer-Encoding: 8BIT
Content-Disposition: inline
Message-Id: <200501282242.58606.oliver@neukum.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 999
Lines: 23

Am Freitag, 28. Januar 2005 21:42 schrieb Josh Boyer:
> Because of various reasons. ?Normal kernel space virtual addresses
> usually start at 0xc0000000, which is where the 3GiB userspace
> restriction comes from. ?
> 
> Then there is the vmalloc virtual address space, which usually starts at
> a higher address than a normal kernel address. ?Along the same lines are
> ioremap addresses, etc.
> 
> Poke around in the header files. ?I bet you'll find lots of reasons.

Probably, this some FAQ, but anyway. The kernel needs physical memory
present and accessible all the time from all contexts. This is mapped into
this area. All other RAM is called High Mem and needs to be specifically
mapped before it can be used from kernel space.

	Regards
		Oliver
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/