Subject: Re: Mapping large framebuffers into kernel space
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jon Smirl <jonsmirl@yahoo.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, kronos@kronoz.cjb.net,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <20030908001716.78049.qmail@web14901.mail.yahoo.com>
References: <20030908001716.78049.qmail@web14901.mail.yahoo.com>
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Date: Mon, 08 Sep 2003 13:28:52 +0100
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> On my system I have 1GB physical and 1GB swap. So there should always be some
> open address space in the 1-4GB kernel address space. Would it be better to map

The kernel address space is 3Gb-4Gb (ie 1Gb sized) giving a 3Gb user
address space.

> The kernel DRM drivers map framebuffers up to 256MB in size into user space.
> Could this be mapped as a single 256MB page instead of 64K 4KB ones?

Well the CPU only has 4K/4Mb as the basic choices but you could map it
using 4Mb pages in theory - in practice its rather complicated because
of the VM handling. 2.6 has some basic stuff for doing this kind of
thing with fixed unswappable memory.

However if your radeon driver is touching the RAM often enough to matter
you have another problem.

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