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Thread: PAE kernel does not see all 4GB of RAM

  1. #21
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    Re: PAE kernel does not see all 4GB of RAM

    Quote Originally Posted by lotuseclat79 View Post
    Hi sanderj,

    I have been mulching over the raw data - only some of which you address in your script, and I would like to suggest a few changes:

    1) the data from the memory map indicates {reserved, usable, ACPI NVS|data}, but it would be useful to the user to see both the reserved below and above 3GB w/4GB or more of RAM.
    2) a computation of potentially recoverable RAM above 3GB w/memory hoisting.

    In my case, the potential is about 3/4 GB!
    OK, good point. So separately show memory above the 0x0000000100000000 = 4.2 GB (in decimal) boundary. Question: is the 0000000100000000 always shown as a boundary, like in my dmesg below?
    Oh wait: your dmesg does show NOT show anything above 0000000100000000 as your BIOS does not understand that, right?



    EDIT:
    Assuming your dmesg does not show anything above 0000000100000000, here's my new script:


    http://wattcher.015.info/check-my-hardware.py


    Can you run that and post the output here?



    Code:
    sander@athlon64:~$ dmesg | grep usable
    [    0.000000]  BIOS-e820: 0000000000000000 - 000000000009f000 (usable)
    [    0.000000]  BIOS-e820: 0000000000100000 - 00000000dbee0000 (usable)
    [    0.000000]  BIOS-e820: 0000000100000000 - 0000000120000000 (usable)
    [    0.000000] e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
    [    0.000000] e820 update range: 00000000dbf00000 - 0000000100000000 (usable) ==> (reserved)
    [    0.000000]  modified: 0000000000010000 - 000000000009f000 (usable)
    [    0.000000]  modified: 0000000000100000 - 00000000dbee0000 (usable)
    [    0.000000]  modified: 0000000100000000 - 0000000120000000 (usable)
    sander@athlon64:~$
    Last edited by sanderj; April 5th, 2010 at 11:21 PM. Reason: URL with updated script

  2. #22
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    Re: PAE kernel does not see all 4GB of RAM

    Hi sanderj,

    Here are several outputs:
    ubuntu@ubuntu:~/Desktop$ dmesg | grep BIOS-e820
    [ 0.000000] BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
    [ 0.000000] BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
    [ 0.000000] BIOS-e820: 00000000000e6000 - 0000000000100000 (reserved)
    [ 0.000000] BIOS-e820: 0000000000100000 - 00000000b7e2fc00 (usable)
    [ 0.000000] BIOS-e820: 00000000b7e2fc00 - 00000000b7e3fc0e (ACPI NVS)
    [ 0.000000] BIOS-e820: 00000000b7f10000 - 00000000b7f30000 (reserved)
    [ 0.000000] BIOS-e820: 00000000b7f30000 - 00000000b7f40000 (ACPI data)
    [ 0.000000] BIOS-e820: 00000000b7f40000 - 00000000b7ff0000 (ACPI NVS)
    [ 0.000000] BIOS-e820: 00000000b7ff0000 - 00000000b8000000 (reserved)
    [ 0.000000] BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
    [ 0.000000] BIOS-e820: 00000000fed13000 - 00000000fed1a000 (reserved)
    [ 0.000000] BIOS-e820: 00000000fed1c000 - 00000000feda0000 (reserved)

    ubuntu@ubuntu:~/Desktop$ dmesg | grep usable
    [ 0.000000] BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
    [ 0.000000] BIOS-e820: 0000000000100000 - 00000000b7e2fc00 (usable)
    [ 0.000000] e820 update range: 0000000000002000 - 0000000000006000 (usable) ==> (reserved)
    [ 0.000000] modified: 0000000000000000 - 0000000000002000 (usable)
    [ 0.000000] modified: 0000000000006000 - 000000000009fc00 (usable)
    [ 0.000000] modified: 0000000000100000 - 00000000b7e2fc00 (usable)

    ubuntu@ubuntu:~/Desktop$ sudo python check-my-hardware.py
    check-my-hardware.py - version: SJ 2009-04-06
    OK, you're root
    ANALYSIS:
    Total of physical memory modules found 4096 MB in 4 memory module(s)
    BIOS offers 2941 MB as usable
    BIOS offers 2941 MB as 'modified' usable
    Memory seen by OS 2896 MB
    BIOS version 10/12/2004
    CPU is PAE enabled
    CPU is 32-bit, and not x86_64 enabled
    OS is 32-bit without PAE
    Summary:
    Memory difference between DIMM hardware and BIOS offering 1155 MB
    Memory difference between BIOS offering and memory seen by OS 45 MB
    Memory difference between DIMM hardware and memory seen by OS 1200 MB
    ADVICE:
    Your BIOS is not offering all of your physical memory. Try to update your BIOS, and/or enable 'memory hole rempapping / hoisting' in your BIOS to get more usable memory

    I'm not really sure what you new output means in my case, since I have only 4GB RAM.

    I was only interested in identifying "potentially recoverable usable" RAM between the highest usable RAM (just under 3GB) and up to 4GB if memory remapping and hoisting is able to recover it.

    So my question is What does the following output mean in those terms?:
    Memory difference between DIMM hardware and BIOS offering 1155 MB
    Memory difference between BIOS offering and memory seen by OS 45 MB
    Memory difference between DIMM hardware and memory seen by OS 1200 MB

    If you could interpret that for your three new lines in those terms, it would be more helpful to the user (at least to me).

    -- Tom

  3. #23
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    Re: PAE kernel does not see all 4GB of RAM

    even if you use pae kernel you have first to enable ram mapping into your BIOS.

  4. #24
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    Lightbulb Re: PAE kernel does not see all 4GB of RAM

    Quote Originally Posted by psusi View Post
    Yes, the PAE kernel can address up to 64gb of physical ram, however many motherboards can not remap physical addresses around reserved blocks. If, for example, your video card is using a 256 meg address in the area just under the 4gb mark, in order to address the physical ram using those same addresses, your motherboard must support remapping those physical ram addresses to higher addresses, otherwise requests to those addresses go to the video card, not the DIMMs. Many motherboards can not do this, so that memory on the DIMMs is not accessible.
    True.

    But my point was that many people are making uninformed and incorrect statements that are easy to check. They, themselves, should check before misinforming the innocent and potentially wasting someones time.
    24 beers in a case, 24 hours in a day. Coincidence? I think not!

    Trusty Tahr 64 bit, AMD Phenom II 955 Quad Core 3.2GHz, GeForce 9600 GT
    16G PC2-6400 RAM, 128 GB SSD, Twin 1TB SATA 7200 RPM RAID0

  5. #25
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    Lightbulb Re: PAE kernel does not see all 4GB of RAM

    Quote Originally Posted by dino99 View Post
    even if you use pae kernel you have first to enable ram mapping into your BIOS.
    Absolutely!

    Without more than 32 bits of hardware memory address space, there is no 4GB+ no matter what OS you use.
    24 beers in a case, 24 hours in a day. Coincidence? I think not!

    Trusty Tahr 64 bit, AMD Phenom II 955 Quad Core 3.2GHz, GeForce 9600 GT
    16G PC2-6400 RAM, 128 GB SSD, Twin 1TB SATA 7200 RPM RAID0

  6. #26
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    Re: PAE kernel does not see all 4GB of RAM

    Tom,

    Would this text be useful:

    Your BIOS is not offering all of your physical memory. You now loose about 1155 MB of memory.
    Try to update your BIOS, and/or enable 'memory hole rempapping / hoisting' in your BIOS to get more usable memory

    Let me know.

  7. #27
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    Re: PAE kernel does not see all 4GB of RAM

    Hi sanderj,

    With a bit more digging, I have isolated the issue to the fact that my MB will not be helped by updating the BIOS because Intel MB w/945 and earlier chipsets do no support memory hole remapping/hoisting in the BIOS.

    But, thanks for all of your effort - I hope I helped to provide feedback that was useful to you with your handy tool.

    I have also been looking into the possibility of reverse engineering the BIOS - lots of new and exciting happenings out there: flashrom and superiotool packages for ubuntu, and the fact that I have 1024 KB of flash ROM and only 64 KB runtime executable - means there is room for improvement, since apparently the so-called Linux BIOS effort now SmartFirmware (CodeGen) and Openfirmware (Firmworks) re: OpenBIOS efforts are making inroads, but the BIOSes w/o memory remapping looks like a neglected market wrt 4GB usage at the user level - unfortunately, due to the other items that need memory either reserved/etc. like PCI, its like there is a focus on new hardware development and an attitude of instead of fixing/retrofitting the BIOS problem - let them buy new hardware. The notion is that with only 4GB of RAM, at most you can probably only hope to use 3.5 w/memory remapping anyway and if you add new hardware to your rig - you lose - unless you have either a 64-bit processor with RAM expansion capability above 4GB (for the hardware addons, etc).

    Thanks,

    -- Tom

  8. #28
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    Re: PAE kernel does not see all 4GB of RAM

    Quote Originally Posted by Slim Odds View Post
    True.

    But my point was that many people are making uninformed and incorrect statements that are easy to check. They, themselves, should check before misinforming the innocent and potentially wasting someones time.
    Quote Originally Posted by Slim Odds View Post
    It is SOOOO easy to find this information these days. You people who keep making incorrect statements need to stop and take a look around before wasting peoples time and leading them in the wrong direction.

    From this page: http://en.wikipedia.org/wiki/Physical_Address_Extension

    Took me about 12 seconds.
    Hi Slim Odds,

    The issue in my case - has not been about the Linux kernel supporting PAE, which it has for some time now, but finding out whether or not my BIOS can be remapped (Intel sucks at telling anyone about this in their documentation). My processor has always supported PAE, but I can't use it even with 4GB due to the limitations of my chipset/MB - and Intel's decision not to upgrade it with memory remapping/hoisting - at least if the would have provided it, I would probably be able to use 3.5GB, but no such luck.

    Further, it appears that BIOS is a neglected area in terms of vendors that just want to push new hardware out the door to make the bottom line this financial quarter.

    Luckily, lots of new things are happening on the BIOS front. See my previous post to this.

    Cheers,

    -- Tom

  9. #29
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    Lightbulb Re: PAE kernel does not see all 4GB of RAM

    Quote Originally Posted by lotuseclat79 View Post
    Hi Slim Odds,

    The issue in my case - has not been about the Linux kernel supporting PAE, which it has for some time now, but finding out whether or not my BIOS can be remapped (Intel sucks at telling anyone about this in their documentation). My processor has always supported PAE, but I can't use it even with 4GB due to the limitations of my chipset/MB - and Intel's decision not to upgrade it with memory remapping/hoisting - at least if the would have provided it, I would probably be able to use 3.5GB, but no such luck.

    Further, it appears that BIOS is a neglected area in terms of vendors that just want to push new hardware out the door to make the bottom line this financial quarter.

    Luckily, lots of new things are happening on the BIOS front. See my previous post to this.

    Cheers,

    -- Tom
    I'm sorry that some people misunderstood my original comment, which was to address these:
    are you using the 32-bit version of PAE Kernel or 64-bit version. 32-bit OS's can not see more then 3GB of RAM. 64-Bit can see as high as 32GB of RAM (i think) This is probably your issue
    Check this site out because 32-Bit OS can not address more then 4GB or RAM. That is the limitation of the OS.
    Which are completely false.
    24 beers in a case, 24 hours in a day. Coincidence? I think not!

    Trusty Tahr 64 bit, AMD Phenom II 955 Quad Core 3.2GHz, GeForce 9600 GT
    16G PC2-6400 RAM, 128 GB SSD, Twin 1TB SATA 7200 RPM RAID0

  10. #30
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    Re: PAE kernel does not see all 4GB of RAM

    Hi Slim Odds,

    We appear to be on the same page:

    While it is true that a 32-bit OS alone cannot address more than 4GB, with a PAE endowed CPU, a 32-bit OS kernel can address up to 36-bits of address space which extends the virtual address space from 4GB to 64GB. Refer to second paragraph at Physical Address Extension.

    However, it is the BIOS limitation of not having memory remapping that restricts the OS from making available usable memory between 3-4GB.

    The interplay between a BIOS and a cpu w/PAE and 4GB of RAM is limited by the ability of the BIOS to memory remap or not with 4GB. If the BIOS vendor would accomodate memory remapping between 3-4GB in a RAM limited to 4GB, then approximately 3.5 GB could potentially be usable - but due to hardware innovations proceeding at a rapid pace, many vendors decided to punt on MBs/chipsets with those limitations.

    Cheers,

    -- Tom

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