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SubjectRe: Best kernel config for exactly 1GB ram
On Sun, Nov 11, 2001 at 02:56:58PM -0600, Steve Bergman wrote:

> Hi,
>
>
> I have just upgraded my athlon 1200 system to 1GB ram. I am unclear as
> to how I should configure the kernel for this box. The config.help says
> to say no to "high memory support" if the kernel will not run on a
> machne with more than 1GB. When I do this I notice that my available
> memory as reported by top is ~ 120MB less than if I say I want 4GB
> support. I recall that linux reserves some of the address space for
> itself (I thought it was just 64MB).
>
> What are the trade offs involved here? Am I better off sacrificing a
> bit of the physical memory for reasons of efficiency elsewhere? When I
> request support for up to 4GB, what exactly changes with respect to the
> visible virtual address space that apps see, etc?
>
> This is a desktop machine, so it's not running Oracle or anything like
> that. I seem to recall Linus mentioning that big databases tend to like
> the large (3GB) virtual address space.

Personally, I'd just leave it at the default no high-mem option.

The kernel will then be able to 'see' about 960MB of the memory, so you loose
about 64MB of it, but it's not worth the kernel using bounce-buffers etc just so
you can get 64MB more memory.

IIRC there was a 2GB patch that just redefined PAGE_OFFSET or something similar,
this means that you could see all the memory, but the max virtual memory a
process could see would be 2 gig (as opposed to 3 gig with the default).

--

Mark Zealey
mark@zealos.org
mark@itsolve.co.uk

UL++++>$ G!>(GCM/GCS/GS/GM) dpu? s:-@ a16! C++++>$ P++++>+++++$ L+++>+++++$
!E---? W+++>$ N- !o? !w--- O? !M? !V? !PS !PE--@ PGP+? r++ !t---?@ !X---?
!R- b+ !tv b+ DI+ D+? G+++ e>+++++ !h++* r!-- y--

(www.geekcode.com)
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