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Re: Large ramdisks, kernel memory space issue

--- "J.A. Bezemer" <j.a.bezemer@opensourcepartners.nl>
> On Fri, 15 Apr 2005, salman h wrote:
> > Hi All,
> >
> > I'm using a slightly modified Debian kernel along
> with
> > PXELinux to boot a machine over the network.
> >
> > My kernel's memory footprint is quite large (400
> megs)
> > because it pre-allocates memory for some processes
> (in
> > the interest of speedier process execution).
> >
> > My ramdisk size is about 500 megs.
> >
> > Now, the ramdisk has to fit in the lower 1 Gig of
> > memory which the kernel can access. So a ramdisk
> > bigger than 500 megs cannot be loaded by the
> kernel,
> > since the ramdisk would exceed the 1 Gig kernel
> memory
> > space bound.
> This 1GB boundary makes me think of the High Memory
> kernel config option. You might want to try
> different values for that option,
> even though they might not be intuitively applicable
> to your case.
> Regards,
>   Anne Bezemer

What you said makes sense. I spent some time reading
up on the memory organization structure of linux. It
lead me to believe that if I enable CONFIG_HIMEM in
the kernel the it would be able to access the entire
4GB memory address space.

I tried that, but no success.

Googling around, I found a simple write-up on kernel
memory organization which had a link to a patch to
split kernel/user memory allocation.

Here is the link to the article:

That didn't work either though. So I'm still fairly
confused about how the kernel manages higher memory.

Perhaps there's a hard upper-limit on the size of the
initial ramdisk? I don't know...

Anyway, another user suggested a feasible sounding
Make the initrd small enough to fit in low mem.
Mount more ramdisks later during the init process
(either by downloading from the server, or from the CD
if using ISOLinux, etc).

I hope that makes sense.

Thanks for your help.


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