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I don't dispute anything you've said HROAdmin but I have first hand seen systems with PAE report a lot less RAM than the physical amount present. There is an overhead ...
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  1. #11
    Linux Guru bigtomrodney's Avatar
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    I don't dispute anything you've said HROAdmin but I have first hand seen systems with PAE report a lot less RAM than the physical amount present. There is an overhead to using this technology which is why I tend to recommend switching to 64-bit. (It's about the only reason so far I can come up with for the switch to 64-bit )

  2. #12
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    ...but I have first hand seen systems with PAE report a lot less RAM than the physical amount present.
    Then it is not configured correctly. PAE does what it has been designed to do - saying that it doesn't is simply untrue.

    The honest answer to anonymoususer is that checking his CPU and recompiling his kernel for PAE support may be beyond his abilities.

    As an example, here is a SLES 9.3 32-BIT image on a system with 6GB of RAM. Results:

    Code:
    uname -a
    Linux SYSTEM_NAME 2.6.5-7.244-bigsmp #1 SMP Mon Dec 12 18:32:25 UTC 2005 i686 athlon i386 GNU/Linux
    Code:
    free -m
                 total       used       free     shared    buffers     cached
    Mem:          5958        125       5832          0         20         61
    -/+ buffers/cache:         44       5913
    Swap:         3074          0       3074
    Code:
    cat /etc/SuSE-release 
    SUSE LINUX Enterprise Server 9 (i586)
    VERSION = 9
    PATCHLEVEL = 3
    Code:
    grep PAE /boot/config-2.6.5-7.244-bigsmp 
    CONFIG_X86_PAE=y
    And here is top sorted by memory usage:

    Code:
    top - 15:42:28 up 15 min,  1 user,  load average: 0.00, 0.08, 0.14
    Tasks:  45 total,   2 running,  43 sleeping,   0 stopped,   0 zombie
    Cpu0  :  0.0% us,  0.0% sy,  0.0% ni, 100.0% id,  0.0% wa,  0.0% hi,  0.0% si
    Cpu1  :  0.0% us,  0.0% sy,  0.0% ni, 100.0% id,  0.0% wa,  0.0% hi,  0.0% si
    
      PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                               
    10463 root      16   0  7856 2404 1956 R  0.0  0.0   0:00.03 sshd                                                                  
     8964 root      16   0  4740 1940 1620 S  0.0  0.0   0:00.06 sshd                                                                  
    10466 root      15   0  3616 1736 1312 S  0.0  0.0   0:00.02 bash                                                                  
     9196 root      21   0  2644 1296 1156 S  0.0  0.0   0:00.00 powersaved                                                            
    10494 root      16   0  1784  924  728 R  0.0  0.0   0:00.00 top                                                                   
     9850 root      16   0  8320  904  728 S  0.0  0.0   0:00.00 nscd                                                                  
    10310 root      16   0 13004  764  636 S  0.0  0.0   0:00.16 ddtp_deviced                                                          
     9848 root      16   0  1600  700  608 S  0.0  0.0   0:00.00 cron                                                                  
     7421 root      17   0  1604  644  556 S  0.0  0.0   0:00.00 resmgrd                                                               
    10304 root      20   0  1628  608  536 S  0.0  0.0   0:00.83 mingetty                                                              
    10305 root      18   0  1628  608  536 S  0.0  0.0   0:00.02 mingetty                                                              
    10306 root      19   0  1628  608  536 S  0.0  0.0   0:00.01 mingetty                                                              
    10307 root      20   0  1628  608  536 S  0.0  0.0   0:00.02 mingetty                                                              
    10308 root      18   0  1628  608  536 S  0.0  0.0   0:00.00 mingetty                                                              
    10309 root      18   0  1628  608  536 S  0.0  0.0   0:00.00 mingetty                                                              
     7099 root      16   0  1532  596  404 S  0.0  0.0   0:00.00 klogd                                                                 
     7078 root      16   0  1420  524  432 S  0.0  0.0   0:00.00 syslogd

  3. #13
    Linux Guru bigtomrodney's Avatar
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    Quote Originally Posted by HROAdmin26 View Post
    Then it is not configured correctly. PAE does what it has been designed to do - saying that it doesn't is simply untrue.
    I apologise, it may well have been that I didn't do it correctly.

    Can I ask though, that is a two CPU machine, does that make any difference to the PAE setup? As in physically the RAM 'bays' are usually tied to CPUs so does this affect how the RAM is addressed?

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  5. #14
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    As in physically the RAM 'bays' are usually tied to CPUs so does this affect how the RAM is addressed?
    No, even if I pull a CPU, I will still have 6GB RAM. While this is a slightly older system with 2 sockets and a CPU in each, most X86 hardware now is 1-2 sockets and anything from 2-8 cores per socket. This "loading up" of multiple cores per socket has mostly invalidated trying to map RAM slots to any given CPU. It is much more prevalent in other architectures like Sparc.

    Clearly, this is an *enterprise* build of this kernel meant for large-memory, SMP systems (hence the kernel name XXX-bigsmp), but the point is that a correctly configured 32-bit kernel can use larger RAM sizes. It is up to the user to determine if that is useful. If you run a database server and the *application* is hitting a 3-4GB process limit, adding more RAM and using PAE will not help much. Your application (with no changes) will hit the same limit.

  6. #15
    Linux Guru bigtomrodney's Avatar
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    Ah I see. Thanks HROAdmin.

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    HRO?

    is what your trying to tell me that I can use 8 gigs and my 32bit system (provided I enable PAE of course) will recognize all 8 gigs It's just no one application will be able to use more than 4 (or 3.2 to be more exact) at a time.

    Cause if that's the case I'm fine with that. I don't plan on using any apps that will take up 4 gigs. just lots and lots of little ones.



    sorry if I'm not getting this by the way

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