Re: Reserving physical memory at boot time

[Duncan Sands <baldrick@wanadoo.fr>]

On Wednesday 04 December 2002 17:44, Mike Galbraith wrote:
> At 08:25 AM 12/4/2002 -0500, Richard B. Johnson wrote:
> >On 3 Dec 2002, Alan Cox wrote:
> > > On Tue, 2002-12-03 at 21:11, Richard B. Johnson wrote:
> > > > If you need a certain page reserved at boot-time you are out-of-luck.
> > >
> > > Wrong - you can specify the precise memory map of a box as well as use
> > > mem= to set the top of used memory. Its a painful way of marking a page
> > > and it only works for a page the kernel isnt loaded into.
> >
> >If you are refering to the "reserve=" kernel parameter, I don't
> >think it works for memory addresses that are inside existing RAM.
> >I guess if you used the "mem=" parameter to keep the kernel from
> >using that RAM, the combination might work, but I have never
> >tried it.
>
> reserve= is for IO ports (kernel/resource.c). I think Alan was referring to
> mem=exactmap.
>
> If Duncan didn't have the pesky requirement that his module work in an
> unmodified kernel, it would be easy to use __alloc_bootmem() to reserve an
> address range and expose via /proc.  But alas...

I actually said I was happy to modify the kernel!  As for __alloc_bootmem(),
based on my quick reading of the implementation in 2.5.50, I don't see how
you can be sure it will give you a particular physical page.  I would like to
either get the page I want, or fail.

Thanks for your help,

Duncan.