x86_64 System with 4GB Ram only seeing 3873 MB

OrangeToque · Last edited by OrangeToque on Thu Nov 22, 2007 6:38 pm; edited 2 times in total

Hello,

I know that there have been similar posts, however I have not been able to find a post that explicitly deals with the amd64 arch.

Here is the problem ::

free reports ::

Jenk · Tux's lil' helper Joined: 18 Sep 2006 Posts: 112

Are you sure you haven't got a config option mixed up somewhere? My 2GB box reports:

CoolBeer · Posted: Thu Nov 22, 2007 10:28 pm Post subject:

Hmm? How do you get that to be only 30MB free?
I read it as atleast 2382MB free.

My box reports:

OrangeToque · Posted: Thu Nov 22, 2007 10:55 pm Post subject:

Correct, there was in fact 2382 Mb free. The issue isn't that I do not have any RAM available, but rather that my system does not recognize all 4032 Mb of system memory.
_________________
OS: Linux 2.6.24-gentoo-r3 x86_64 Gentoo v1.12.11.1 Sound: HDA Intel
CPU: Intel(R) Core(TM)2 Quad CPU Q6700 @ 2.66GHz GenuineIntel
Disk: 2x 300GB 7200.10 SATA II Video: GeForce 7900 GT RAM: 4GB

PaulBredbury · Watchman Joined: 14 Jul 2005 Posts: 7310

Could be a memory hole caused by the BIOS, for its own needs or bugginess. Anyway, I wouldn't worry about it unless it was >=512mb. RAM is cheap, and the stability of a PC is far more important.

paulb787 · Apprentice Joined: 14 Nov 2005 Posts: 250

same prob

3.8Gb is just not 4GB.. lol

m4yer · n00b Joined: 13 Apr 2007 Posts: 13 Location: GER

and same here ... 3954mb ...

schachti · Posted: Wed Jan 02, 2008 11:10 am Post subject:

What is your output of

eccerr0r · Posted: Wed Jan 02, 2008 10:23 pm Post subject:

"(not me too)"

I'd gladly trade my not-so-stable motherboard for one of yours that have less than 4GB shown:

selig · Posted: Fri Jan 04, 2008 9:24 am Post subject:

I am not completely sure, but IMHO kernel memory is not displayed by "free" and thus it reports less memory available. If you have got a bloated kernel, like on a RHEL x86_64, it eats up e.g. 128 MB (on my 16 GB machine). On my laptop with 768 MB, my hardened x86 Gentoo kernel eats up only about 30 MB. The size varies among systems - I should do a test on one hardware with vastly different kernels, because it may be just BIOS instead of kernel...

mattst88 · Developer Joined: 28 Oct 2004 Posts: 423

This is a problem interpreting the units.

A kilobyte is 1000 bytes. This is the base 10 system.
A kibibyte is 1024 bytes. This is the base 2 system.

I'm guessing you have 4096 MiB of RAM and 64 MiB allocated to graphics. This means you've got 4032 MiB of system memory. 4032 MiB is around 3845 MB of memory. I don't know where the difference of 30 or so MB is, but the fundamental problem is a misunderstanding of the units.

selig · Posted: Sat Jan 05, 2008 2:38 pm Post subject:

I do not think this is the case... on my 2GB amd64 system, the difference is 35 MB - on a different amd64 system with 2 GB RAM the difference was 36 MB. I compiled both kernels so they should be approximately the same (I always choose the same options, only some drivers are different, depending on the hardware configuration).

As I mentioned earlier, with RHEL the difference was 128 MB (albeit on a 16 GB machine). I think that this really is the kernel size, because the Red Hat kexec documentation states that you need to allocate min. 128 MB for the kexec kernel.
If it were the difference between 1000 and 1024 kilo/mega/giga bytes, on a 16384 "MB" machine it would mean you get only 15.3 GB - which most certainly is not the case. Anyway, I can look at the reported memory sizes on a lot of different machines running the same kernels when I get back to work on Monday.

selig · Posted: Sun Jan 20, 2008 11:06 am Post subject:

You can check the amount of memory eaten by the kernel by issuing this command:

wyvern5 · Apprentice Joined: 11 Nov 2006 Posts: 161

This is almost certainly caused by the BIOS memory hole issue. Much less of an issue on 64bit (32bit windows sees my 4gb as 2.7gb), though. I see 3943 as total mem from free -m. I wouldn't worry about it.