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Old 01-06-2005, 05:50 PM   #1
rex67
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linux memory limit?


I have a java application on linux that has extensive caching. My server has about 8GB of memory installed, but I've been told there is a linux limitation to only use about 2GB. If this is true, is there any way to increase this to use the full 8GB?

redhat 9

uname -a
2.4.20-8smp #1 SMP Thu Mar 13 17:45:54 EST 2003 i686 i686 i386 GNU/Linux

BEA WebLogic JRockit(TM) 1.4.2_03 JVM (build ari-24879-20031212-1523-linux-ia32, Native Threads, GC strategy: parallel)
 
Old 01-06-2005, 06:22 PM   #2
rex67
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To answer my own question, I found a useful link regarding this problem at theserverside:

http://www.theserverside.com/discuss...hread_id=26347
 
Old 01-06-2005, 07:07 PM   #3
vectordrake
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large memory

More ofa 4GB limit, I think, but its more of a 32 bit problem than a Linux problem. According to the messages traded back and forth on the Linux Kernel Archive it seems that you can use that memory. Does your machine have more than 1 processor?
 
Old 01-06-2005, 09:33 PM   #4
carl0ski
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4GB in the physical restriction of 32bit processors
linux support up to that amount provided your Bios support 4gig ram

2Gig is the file size limit of the EXT2 filesystem

AMD 64 on a 64bit distro/kernel will support a few terabytes of ram not sure exact figure.

unless java VM machine has a seperate limit on RAM it can use?

Mandrake has some kernels available that says
P3 >4gB so i guess there must be a custom kernel to let you use all the ram.

use Urpmi to find the kernel with more memory support.
or other means
 
Old 01-07-2005, 04:59 AM   #5
vectordrake
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You hit the nail on the head. And, yes there are big memory kernels that take advantage of larger RAM sizes. The 4GB limit is per process, so if your apps is moltithreaded, you should be able to access the memory.

The kernels being referred to have the BigMem option turned on. In the config, you find that here:
Code:
Processor type and features  --->High Memory Support (on)  --->(X)4GB ##or (X)64GB)
If the option is checkedat compile time, you've got big memory support. If not (like on my workstation with 384mb), its compiled without. The kernel runs faster without the big memory support turned on on machines with less RAM but you cannot use all your RAM with that kernel if you go above that amount (~800mb),(4GB),(64GB). I think that the option can actually be extended to a few TB, but you have to have a multi processor machine in order to be able to handle that many big processes.

If I've misunderstood the concept, will someone please correct me.
 
Old 01-07-2005, 05:39 AM   #6
MasterC
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On a related note, AFAIK Sun has not yet released a JRE/JDK/JVM to run on 64bit. Feel free to prove me wrong, this was something I seem to remember reading about a week ago.

Cool
 
Old 01-07-2005, 09:36 PM   #7
vectordrake
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Quote:
Originally posted by MasterC
On a related note, AFAIK Sun has not yet released a JRE/JDK/JVM to run on 64bit. Feel free to prove me wrong, this was something I seem to remember reading about a week ago.

Cool
I think that Sun can prove you wrong (that's hard to do - I have read a lot of your posts). Check out This page about the new j2se5.0 (yeah, what happened to 1.5???). You'll see that 64 bit IS supported, as long as you're using Linux and AMD...
 
Old 01-08-2005, 03:09 AM   #8
MasterC
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Thanks for link, linking further a bit, it must have been the plugin I read about:
http://java.sun.com/j2se/1.5.0/insta...l#requirements

Cool
 
Old 01-08-2005, 03:26 AM   #9
rex67
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not 64 bit

would be nice
 
Old 01-08-2005, 03:36 AM   #10
vectordrake
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Heh. I wouldn't have known if I hadn't just installed it myself for my 32 bit (or is that 2-bit!) machine and happened to read the whole page.
 
  


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