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Old 11-24-2010, 04:51 PM   #1
pyroman59
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RHEL 5.3 Dell 1750s not seeing 8GB RAM


I have a rack of Dell 1750s running RHEL 5.3 and we just upgraded the memory from 4GB to 8GB. When the machine boots, the BIOS probes out 8GB, but the boot scroll (dmesg) only shows 4GB, as seen after we login. How can I get it to see all of the mem?
 
Old 11-24-2010, 05:00 PM   #2
AlucardZero
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Are you running a 32 bit kernel or 64 bit?

If 32, try the PAE kernel.
 
Old 12-02-2010, 11:46 AM   #3
pyroman59
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It is 32 bit. So it is not anything to do with maybe the BIOS needs upgrading? It is really old.
 
Old 12-02-2010, 11:51 AM   #4
lazlow
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You either need to switch to a PAE kernel or switch to 64bit. Since you have a rack I would try both and see what is faster. When you use 32bit each application is limited to 3.2Gb(about).
 
Old 12-02-2010, 11:57 AM   #5
pyroman59
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OK, thanks for responding.
 
Old 12-02-2010, 12:01 PM   #6
szboardstretcher
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32bit Linux can only address up to 3gb of ram.
 
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Old 12-02-2010, 12:04 PM   #7
pyroman59
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Thanks SZboardstretcher!
 
Old 12-02-2010, 12:09 PM   #8
lazlow
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32bit CAN address more than 3gb of ram, IF you use a PAE kernel. However(if I was not clear above) even with a PAE kernel each apllication can only address about 3Gb. With 8Gb of ram and a PAE kernel you could have two applications using 3Gb each and still have plenty of ram for buffers(etc).
 
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Old 12-02-2010, 12:14 PM   #9
szboardstretcher
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Post

Quote:
Originally Posted by lazlow View Post
32bit CAN address more than 3gb of ram, IF you use a PAE kernel. However(if I was not clear above) even with a PAE kernel each apllication can only address about 3Gb. With 8Gb of ram and a PAE kernel you could have two applications using 3Gb each and still have plenty of ram for buffers(etc).
To be clear, I meant- "Using a regular 32bit Kernel on a 64bit CPU, will only allow you access to 3Gb of ram."

You are correct that PAE will allow you access to more.

According to WikiPedia @ http://en.wikipedia.org/wiki/Physical_Address_Extension

Quote:
"This, theoretically, increases maximum physical memory size from 4 GB to 64 GB. The 32-bit size of the virtual address is not changed, so regular application software continues to use instructions with 32-bit addresses and (in a flat memory model) is limited to 4 gigabytes of virtual address space. The operating system uses page tables to map this 4-GB address space into the 64 GB of physical memory. The mapping is typically applied differently for each process. In this way, the extra memory is useful even though no single regular application can access it all simultaneously."

Last edited by szboardstretcher; 12-02-2010 at 12:16 PM.
 
Old 12-02-2010, 12:18 PM   #10
lazlow
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The important part is this:

Quote:
In this way, the extra memory is useful even though no single regular application can access it all simultaneously."
Which is what I was trying to explain.
 
  


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