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sub_pop_culture

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22 years ago

S

sub_pop_culture

3 Posts

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9640

May 11th, 2005 22:00

Linux on a P370 with 4GB RAM

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
  • C

    Chipstone

    525 Posts

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    0

    Posted May 12th, 2005 10:00

    It is my understanding that 32 bit operating systems, in theory, will address up to 4GB of memory. But in reality the operating system is only able to access approximately 3.2GB of full 4GB of memory.

    However, 64 bit operating systems will address, I believe all the way up to 16TB of memory.

    I have 4GB of installed memory and Windows XP (32 Bit) reports 3.2GB of memory, Windows XP x64 reports the full 4GB.

    Message Edited by Chipstone on 05-12-2005 07:26 AM

  • S

    sub_pop_culture

    3 Posts

    150

    0

    Posted May 12th, 2005 14:00

    I thought there was a patch for Linux though, that allowed it to see more. Or is it more a limitation of the hardware?
  • C

    Chipstone

    525 Posts

    150

    0

    Posted May 12th, 2005 17:00

    I believe the restriction is on the software. If it was a hardware issue my Windows x64 would not have reported the full 4GB of installed memory.

    If is not an issue with Linux operating systems then you are missing the patch to allow the system to read above 3GB or maybe a parameter that need to be added to the boot-up sequence.
  • N

    npgall

    26 Posts

    150

    0

    Posted May 15th, 2005 21:00

    Hi sub_pop_culture,
     
    I am not a Linux expert (I see myself as an intermediate, but that may be an overstatement). I've been working with a couple of machines with over 4GB of RAM, with both 2.4 series kernels and subsequently 2.6 series kernels.
     
    The 2.4 series kernels cannot properly address 4GB memory. The 2.6 series can. I think the limitations are based in OS software primarily. I've been running memory intensive java webserver applications on these machines. On a 2.4 kernel, performance was dismal and I could not allocate more than 1.5 GB (approx) memory to the JVM. On 2.6, performance is far better and I can allocate above 2GB.
     
    I think a kernel upgrade should improve your situation. Eventually, 64-bit operating systems will solve the problem.

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