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Old 01-23-2008, 10:04 AM   #1
atlastc
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CentOS - Kernel Memory Recognition Issue


I've got a system with the following:

Motherboard: Gigabyte GA-M57SLI-S4
RAM: 8GB (4 x 2GB)
OS: CentOS 4.6 + Updates
Kernel: Linux [systemname] 2.6.9-67.0.1.ELsmp #1 SMP Wed Dec 19 15:19:57 EST 2007 x86_64 x86_64 x86_64 GNU/Linux

On POST, the system shows memory as 8388608K. In the BIOS, base memory is 640K and extended memory is 8191M.

However, when I boot into the system, only about 6.7GB of ram is usable:

<snip of dmesg>
Memory: 6627032k/7602176k available (2126k kernel code, 0k reserved, 1313k data, 212k init)
<snip>

<snip of free>
total used free shared buffers cached
Mem: 6627648 1847752 4779896 0 10608 1657160
-/+ buffers/cache: 179984 6447664
<snip>

<snip of /proc/meminfo>
MemTotal: 6627648 kB
MemFree: 4779896 kB
Buffers: 10640 kB
Cached: 1657400 kB
SwapCached: 0 kB
Active: 1349192 kB
Inactive: 382868 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 6627648 kB
LowFree: 4779896 kB
SwapTotal: 10482404 kB
SwapFree: 10482404 kB
Dirty: 76 kB
Writeback: 0 kB
Mapped: 1259276 kB
Slab: 22392 kB
CommitLimit: 13796228 kB
Committed_AS: 450684 kB
PageTables: 4268 kB
VmallocTotal: 536870911 kB
VmallocUsed: 267764 kB
VmallocChunk: 536603127 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 2048 kB
<snip>

Based on some suggestions I've found, I've tried adding mem=10G and mem=8G to the kernel boot parameters with no luck.

I've also tried CentOS 5.1 with the same results.

There also don't appear to be any options in the BIOS that allow me to tweak my memory settings, but the system itself *appears* to recognize the full 8GB.

Does anyone have any ideas as to what I should try next? Any input is greatly appreciated.

Regards,

Nate D.
 
Old 01-23-2008, 11:47 AM   #2
Lenard
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For CentOS 5 install the PAE kernel; yum install kernel-PAE

For CentOS 4 install the kernel-hugemem; yum install kernel-hugemen --enablerepo=centosplus

Better yet use the 64-bit version of either, as the 64-bit kernel does not have this memory issue.
 
Old 01-23-2008, 02:05 PM   #3
lazlow
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Lenard

Look again. He is running 64bit.
 
Old 01-23-2008, 02:40 PM   #4
Lenard
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Your right, my mistake...........sorry to atlastc and thanks to you lazlow for correctin me.
 
Old 01-23-2008, 03:25 PM   #5
johnsfine
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IIUC, your motherboard has integrated graphics. That takes a chunk of your main memory. It's hard to believe it takes that big a chunk.

I downloaded the manual for your motherboard (I'm trying to select a motherboard for a new Linux system myself, so I'm downloading a lot of motherboard manuals). I was surprised that manual gives no hint how you manage the amount of memory used by the integrated graphics.

The Asus motherboard I recently purchased for my son's Windows XP system at least gives a method of managing that. It fails to explain what the BIOS choices really mean and how they interact with Windows Driver choices, but at least there is a hint. It seems to have the ability to take up to a GB of ram for integrated graphics if you want to. I can't imagine why you would want to, and that certainly isn't the default, and you seem to be losing even more than a GB. So, I may be barking up the wrong tree.

Also, I've seen BIOS choices in many motherboard manuals for controling the size of the hole they put in the address space (I think near the end of the first 4GB). I never understood that issue (what it is for, how it interacts with Windows or Linux, etc.) and I don't seen any discussion of it in your Motherboard manual.
 
Old 01-23-2008, 03:45 PM   #6
atlastc
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Lenard: No worries on the arch mismatch, but FWIW, I was originally running Centos 4.6 x86 with kernel-smp and it recognized the same (6.7GB) amount of RAM. I rebuilt the system as x86_64 to try and remedy the problem with no luck.

johnsfine: Hrm, I've got this motherboard in multiple systems and none of them have onboard video. I'm using a 512MB PCI-e video card in them. The only thing I can think of that *might* give me any memory management options in the BIOS would be a BIOS update but I don't know if a) any updates exist and b) if any updates will render my board(s) useless. (BIOS updates and I have a rotten history so I usually use them as a last resort)

I'm aware of the fact that there can be a memory-management "gap" where up to 2GB of the initial 4GB of memory can be reserved. That's why I was trying to attempt the mem=10GB boot option. I found the suggestion here:

http://www.linuxquestions.org/questi...gb-ram-592832/

I'd love to figure this out, because RAM issue asside, the system screams. I've got one running (5) VMware-Server virtual machines & it stays around 80-85% idle with very minimal CPU I/O wait states (having a 3ware PCI-e 9660 helps).
 
Old 01-23-2008, 04:12 PM   #7
lazlow
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Atlastc

I think the 7602176k to 8388608K drop is probably due to the video sharing thing. The 6627648k to 7602176k drop is another issue. You might try playing around with the bios hole setting to see if that will effect anything. The other guess would be to go over to the Centos forum and see if they have any ideas.

Edit: I could not find the 9660 on 3wares site. Are you sure that is the correct model #? It could be that this card is taking up the memory before the OS even sees it.

Last edited by lazlow; 01-23-2008 at 04:28 PM.
 
Old 01-23-2008, 04:30 PM   #8
johnsfine
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Atlastc, I followed that link about the memory-management "gap" (because I want to set up a similar system myself soon) but I didn't understand it. If you find any clearer explanation, please report it back to this thread.

Lazlow, I'm pretty sure the 7602176k represents physical ram plus swap file, so it should be ignored for this discussion. I think the ram size is 6627648.
 
Old 01-23-2008, 05:36 PM   #9
lazlow
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John

Quote:
I'm pretty sure the 7602176k represents physical ram plus swap file, so it should be ignored for this discussion. I think the ram size is 6627648.
I do not think that(above) can be correct. My F8-64bit has this dmesg

Quote:
Memory: 2059304k/2097088k available (2442k kernel code, 37396k reserved, 1381k data, 324k init)
I have 6 gigs of swap.

Also what model of the 3ware card are you using? I can find a 9650 but not 9660. Edit:OOOps this part should be to Atlastc

Last edited by lazlow; 01-23-2008 at 07:22 PM.
 
Old 01-23-2008, 07:15 PM   #10
johnsfine
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Quote:
Originally Posted by lazlow View Post
I do not think that(above) can be correct.
Oops. You're right.
 
Old 01-24-2008, 09:36 AM   #11
atlastc
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Lazlow: The 9660 was a typo - I meant 9650 (http://www.3ware.com/products/serial_ata2-9650.asp). The 3ware 9650 has 256MB of onboard DDR2 memory used for write-caching which really helps performance. I've got an (8) port 9650 in a different motherboard that doesn't have these RAM issues.

Unfortunately my BIOS is very basic and doesn't have anything geared towards messing around with memory (that I can find). There's an entire screen dedicated to overclocking (and I could overclock the RAM config), but again, the BIOS *seems* to be reporting the full 8GB.

Johnsfine: The best I could come up with on the memory mapping is this:

http://en.wikipedia.org/wiki/Memory-mapped_I/O

As I understand it, your motherboard (or OS, I guess) can reserve portions of RAM for various functions, thus leaving less for normal system operations. I think the poster from my previous link was trying to show ways of tricking the kernel into handling memory differently(?)

I've cross-posted this into the CentOS 4 hardware forums, but they're kind of quiet & I've received no responses:

http://www.centos.org/modules/newbb/...forumpost40317

So for now, I'm still stumped. I need a coffee.
 
Old 01-24-2008, 10:21 AM   #12
atlastc
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I just went over to take another look at the system/BIOS to gather more info. The motherboard version is 1.0 and the running BIOS is "F4". If you look at this link:

http://tw.giga-byte.com/Support/Moth...ProductID=2287

You'll see that they're currently at BIOS revision "F12" and at "F5" they list "Improve DDR2 compatibility"...

So I'm wondering if a BIOS update would a) potentially address this issue and b) give me more options to tweak memory settings...

I also scoured through the BIOS again - there are absolutely no onboard video options (there is no actual onboard video port). The only "tweaking" options are under the "MB Intelligent Tweaker" section, but it mainly deals with CPU/RAM voltage and clock speed...

I'm not so sure I want to try a BIOS update because I don't have any spares of this particular model. I'll have to ponder this one.
 
Old 01-30-2008, 11:54 AM   #13
ordinary
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I have very similar problems with a very similar setup. My board is rev2 of the GA-M57SLI-S4, the OS is Fedora 8 (x86_64), and I have 4GB (i.e. 4x1) of memory. The BIOS recognizes all 4GB, but free and the system monitor report only ~3.2GB.

I posted a question to FedoraForum on this subject, and I responded to the thread on the CentOS forums as well. There is also another similar thread here at LinuxQuestions.

For those interested, this board has no onboard video.

This system was upgraded from 2GB (i.e. 2x1) to 4GB (4x1). When I first booted into the BIOS after adding the other two 1GB sticks, the BIOS only reported ~3.2GB. After I reset the CMOS and rebooted into the BIOS, it reported all 4GB. Fedora still only sees ~3.2, however.


Has anybody found an answer to this problem yet?

Thanks,
Phil

Last edited by ordinary; 01-30-2008 at 11:57 AM.
 
Old 01-30-2008, 12:01 PM   #14
lazlow
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Ordinary

Are you running 32bit or 64bit?
 
Old 01-30-2008, 03:35 PM   #15
ordinary
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Quote:
Originally Posted by lazlow View Post
Ordinary

Are you running 32bit or 64bit?
Lazlow, thanks for your interest. As I stated, I am running Fedora 8 x86_64. I guess that it may not be obvious that's the 64 bit version.

Actually, I think I have managed to fix my problem. I think it was a buggy and lying BIOS. Sometimes it would show 4095MB extended memory and sometimes 3327MB depending on its mood. That was BIOS FE for the Gigabyte GA-M57SLI-S4 rev2 (to which I had upgraded for its virtualization support). Updating to BIOS FFC (published 4 Jan 2008) seems to have fixed my memory access problem, and now I can see all of my new memory. Maybe this info will help someone else.

Phil
 
  


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