I have a few P370s running Red Hat Enterprise 3 Update 3 with 4 1GB DIMMs in them. The BIOS correctly sees 4GB of system memory, but when the OS boots up, it sees only 3GB.
I have looked through the /boot/config-2.4.21-20.EL file, and found:
CONFIG_HIGHMEM4G=y

One would assume that this would enable the system to see 4GB of memory right?
Does CONFIG_3GB=y have anything to do with limiting the system to 3GB? The menuconfig for the kernel sources has no help section for the CONFIG_3GB option.
So what might be the cause of this missing memory?

Output of uname -a:
Linux testlinux 2.4.21-20.EL #1 Wed Aug 18 20:58:25 EDT 2004 i686 i686 i386 GNU/Linux

/proc/meminfo:
total: used: free: shared: buffers: cached:
Mem: 3159224320 1165672448 1993551872 0 148643840 461938688
Swap: 4293586944 0 4293586944
MemTotal: 3085180 kB
MemFree: 1946828 kB
MemShared: 0 kB
Buffers: 145160 kB
Cached: 451112 kB
SwapCached: 0 kB
Active: 754948 kB
ActiveAnon: 295044 kB
ActiveCache: 459904 kB
Inact_dirty: 103344 kB
Inact_laundry: 31128 kB
Inact_clean: 0 kB
Inact_target: 177884 kB
HighTotal: 2226728 kB
HighFree: 1468136 kB
LowTotal: 858452 kB
LowFree: 478692 kB
SwapTotal: 4192956 kB
SwapFree: 4192956 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 4096 kB

Did you find any usefull information about this topic.

Please keep me updated.

Also Check this link
http://www.spack.org/wiki/LinuxRamLimits

Actually, that wiki page answers my question.
RHEL3 is running the 2.4 kernel, so I'd assume the reason only 3GB is being seen is because the kernel is reserving 1GB for itself.

RedHat have a hughmem kernel that has a 4GB-4GB split. This should see more.


lxtwin