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.
Any enlightenment would be greatly appreciated.
Thanks,
Steve Bergman
[email protected]
le dim 11-11-2001 ? 21:56, Steve Bergman a ?crit :
> 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
Actually it's a bit less than 1GB, so you'd better go for 4GB support.
Xav
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
[email protected]
[email protected]
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--
(http://www.geekcode.com)