Use a HIGHMEM enabled kernel

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4 total messages Started by Gary Menna Wed, 11 Dec 2002 06:25

#29

Author: Gary Menna
Date: Wed, 11 Dec 2002 06:25

11 lines
1343 bytes

Hi All ,
    I am running Redhat 7.3 on a Compaq with 1 GB RAM    2.4.18-10smp
I get the following message :
Use a HIGHMEM enabled kernel.
896MB LOWMEM available

I thought highmem enabled kernel was only required for =>4GB  RAM
Can anyone enlighten me on this .

Thanking You ,
                    Gary .

Re: Use a HIGHMEM enabled kernel

#30

Author: will
Date: Wed, 11 Dec 2002 08:24

38 lines
2458 bytes

Gary Menna <gary.menna@cmc.cwo.net.au> wrote:

> I am running Redhat 7.3 on a Compaq with 1 GB RAM    2.4.18-10smp
> I get the following message :
> Use a HIGHMEM enabled kernel.
> 896MB LOWMEM available
> 
> I thought highmem enabled kernel was only required for =>4GB  RAM
> Can anyone enlighten me on this .

from Documentation/Configure.help (in the kernel source tree) :

CONFIG_NOHIGHMEM
  Linux can use up to 64 Gigabytes of physical memory on x86 systems.
[......]

  If you are compiling a kernel which will never run on a machine with
  more than 960 megabytes of total physical RAM, answer "off" here (default
  choice and suitable for most users). This will result in a "3GB/1GB"
  split: 3GB are mapped so that each process sees a 3GB virtual memory
  space and the remaining part of the 4GB virtual memory space is used
  by the kernel to permanently map as much physical memory as
  possible.

  If the machine has between 1 and 4 Gigabytes physical RAM, then
  answer "4GB" here.
[......]

your kernel has probably been compiled using the default of "off" - which 
means 960MB is available - which would probably work out right with the
"896MB LOWMEM available" message (the rest of the 960MB is being used for 
kernel code, buffers, stack, etc...)

is it worth recompiling the kernel for that last 40MB? ;-)

will

--

Re: Use a HIGHMEM enabled kernel

#31

Author: will
Date: Wed, 11 Dec 2002 10:35

11 lines
1459 bytes

will@xxxx.swaggie.net wrote:

> is it worth recompiling the kernel for that last 40MB? ;-)

reading this later, i thought it was kinda funny that that 40MB of unused
ram is over 3 times as much ram as the total ram i've got in the laptop
i'm writing this on (a 7-year-old digital hinote, with 12MB ram)!

will

--

Re: Use a HIGHMEM enabled kernel

#28

Author: D. Stussy
Date: Wed, 11 Dec 2002 23:10

24 lines
2239 bytes

EXACTLY 1Gb or below doesn't really need HIGHMEM.

include/asm-i386/page.h:  Change "128" to "16" on line 87 for __VMMALLOC_RESERVE
seems to do the trick on maximizing usable ram.

You'll still lose the top 16Mb.  I found that the system will lock up if one
goes below that number.  For those systems with video on the motherboard, the
top 8Mb is lost anyway (in the minimum video configuration), and giving the
video the top 16Mb still works.

A friend of mine and I have done this on multiple machines and there have been
no system crashes for several months.  We can't testify to longer periods
because we rebooted them to install updated kernels.

On Wed, 11 Dec 2002, Gary Menna wrote:
>    I am running Redhat 7.3 on a Compaq with 1 GB RAM    2.4.18-10smp
>I get the following message :
>Use a HIGHMEM enabled kernel.
>896MB LOWMEM available
>
>I thought highmem enabled kernel was only required for =>4GB  RAM
>Can anyone enlighten me on this .
>
>Thanking You ,

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