memory usage in linux

[strudl]

I have redhat 7.3 on a machine with 3.6Gb memory, how much can linux see and or use ? how can I configure it to use all of it. At the moment it seems to only see 2Gb, which is not enough for my applications.

[bandwidth_pig]

Whoa. That is some serious memory. I thought the kernel supported 4 GB by default.

[tmcG]

You could try passing your memory size to the kernel at boot up and see if that works.

If you use LILO as your boot manager, you can type

# linux mem=3686M

and see what happens!

I used to have to do this with a PC I had that had two 64Mb SDRAM sticks and had to use the linux mem=128M to get linux to detect all the RAm

If it works, you could add it to the append line of your lilo.conf file

I hope this helps!:)

[RedMap]

Is there a way to pass the information using GRUB if it doesn't have LILO?

[oliver2004]

Hi,

when configuring the kernel for compilation, there is an option under "Processor type and features":

CONFIG_NOHIGHMEM

The online help for it says:

---------------------------------
CONFIG_NOHIGHMEM

Linux can use up to 64 Gigabytes of physical memory on x86 systems.
However, the address space of 32-bit x86 processors is only 4
Gigabytes large. That means that, if you have a large amount of
physical memory, not all of it can be "permanently mapped" by the
kernel. The physical memory that's not permanently mapped is called
"high memory".

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.

If more than 4 Gigabytes is used then answer "64GB" here. This
selection turns Intel PAE (Physical Address Extension) mode on.
PAE implements 3-level paging on IA32 processors. PAE is fully
supported by Linux, PAE mode is implemented on all recent Intel
processors (Pentium Pro and better). NOTE: If you say "64GB" here,
then the kernel will not boot on CPUs that don't support PAE!

The actual amount of total physical memory will either be auto
detected or can be forced by using a kernel command line option such
as "mem=256M". (Try "man bootparam" or see the documentation of your
boot loader (grub, lilo or loadlin) about how to pass options to the
kernel at boot time.)

If unsure, say "off".

---------------------------------

hth,

[shadov]

Originally posted by RedMap
Is there a way to pass the information using GRUB if it doesn't have LILO?
Yes it is possible. I don't have GRUB here, so I can't check how, but it's not difficult.

[Hayl]

add it (mem=whatever) to the end of the kernel line in your /boot/grub/grub.conf (or menu.lst)