From: Oliver Neukum <oliver@neukum.org>
To: Josh Boyer <jdub@us.ibm.com>
Cc: John Richard Moser <nigelenki@comcast.net>, linux-kernel@vger.kernel.org
Subject: Re: Why does the kernel need a gig of VM?
Date: Fri, 28 Jan 2005 22:42:58 +0100 [thread overview]
Message-ID: <200501282242.58606.oliver@neukum.org> (raw)
In-Reply-To: <1106944969.7542.13.camel@windu.rchland.ibm.com>
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
next prev parent reply other threads:[~2005-01-28 21:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-28 20:06 Why does the kernel need a gig of VM? John Richard Moser
2005-01-28 20:42 ` Josh Boyer
2005-01-28 20:48 ` John Richard Moser
2005-02-01 15:15 ` Bill Davidsen
2005-01-28 21:42 ` Oliver Neukum [this message]
2005-01-28 20:44 ` Chris Friesen
2005-01-29 1:32 ` Andy Isaacson
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