Re: Max. Physical Memory Amount
christophe.leroy5@capway.com
Fri, 15 Jan 1999 15:53:27 +0100
> With a friend I've setup a 4 CPU Compaq Proliant 5500 (Don't pin me down
> on that number, I'd have to recheck; it's just some rack mounted high
> availability hardware) using a standard 2.0.36 based linux distrib. Well,
> we added the new Compaq diskarray driver (had to use a little bit older
> diskarray controller, as that is the only one supported), and the machine
> now nicely works under linux standalone on a part (48gig) of an external
> Raid-5 drive bay.
>
> Problem is, the kernel explicitly refuses to accept more than 1Gig of
> main memory.
>
> Now, my question is: Is there a very good reason for this (I can see you
> might not get 4G of physical memory for some reasons, but I'd have
> expected at least 3G to work.) ?
>
> I checked the source, and it appears to be a simple sanity check in
> head.c. Can I savely remove it, what is the highest memory amount I can
> hope to work w/o a crash?
>
> I noticed the decent development kernels handel this different. It seems
> they would go almost up to 4GB. Is that right?
>
> Even if so, I'd be happy if I could avoid installing yet another kernel on
> that machine (I don't want be forced to modify the rest of the
> installation due to 2.0 2.2 incompats), so if hacking the 2.0.36 would
> work I'd be more happy.
>
> Is there anyone out with an advice to us?
>
As far as i've understood, the problem is that Linux uses a single
memory descriptor and 32 bits pointeurs. You then have 4Go total
memory space, and you have to dissociate Physical memory and
Virtual memory. Programs are using virtual memory.
The more you have physical memory, the less you have virtual
memory. In order to let programs have 3Go virtual memory, limit of
physical memory has been set to 1Go.
If you want more memory, you have to review memory managing in
Linux.
christophe
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