Only 2.9GB of 4GB available to 2.6.19-1.2911.fc6PAE kernel...

[sbannerman]

All,

I apologize if this has been answered elsewhere...I've looked but haven't yet been able to find anything definitive.

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I have a dual processor Intel Desktop Board (D915GAV) with 4GB of physical memory installed. According to /proc/cpuinfo, both processors have PAE (physical address extension) capability.

[root@adam:~]# cat /proc/cpuinfo |grep pae
flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe constant_tsc pni monitor ds_cpl cid xtpr
flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe constant_tsc pni monitor ds_cpl cid xtpr

At bios initialization, the 4GB is "recognized" by the BIOS.

At kernel selection time (grub), most (but not all) of the 4GB appears to be available. On the grub screen, it shows ~600KB lower and ~3GB upper.

Once operational, only ~2.9GB appears to be available (according to /proc/meminfo and "free -m").

[root@adam:~]# cat /proc/meminfo |grep MemTotal
MemTotal: 2976264 kB
[root@adam:~]# free -m
total used free shared buffers cached
Mem: 2906 708 2198 0 26 434
-/+ buffers/cache: 247 2658
Swap: 1983 0 1983

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As a side note, I have VMWare installed on the machine as well. When I edit a virtual machine within it, it shows that there's a maximum of 3.6GB. This seems consistent with the grub info (600KB + 3GB) but has me confused as to how much memory is actually available within linux.

Can anybody help me understand why the full 4GB doesn't seem to be available?

Cheers

[SlowJet]

Because it is reffering to Virtual Address space. The 4GB arreses are 3 for programs, 1 for the kernel.
The largest single program can be 2.9 GB.

But the real 4GB will be used. Make sure you have lots of swap space to allow the VS and tempfs to do their thing.

Swap space is a good thing, not wasted space. You need 4 or 8GB.

SJ

[JN4OldSchool]

Because it is reffering to Virtual Address space. The 4GB arreses are 3 for programs, 1 for the kernel.
The largest single program can be 2.9 GB.

But the real 4GB will be used. Make sure you have lots of swap space to allow the VS and tempfs to do their thing.

Swap space is a good thing, not wasted space. You need 4 or 8GB.

SJ

Do you have any links to justify this statement? I would like to read up on this as all the information I have seen pretty much says that anything over 1GB of swap is just a waste unless you are preforming some serious number crunching. I have yet to find a single source to recomend 4GB let alone 8GB of swap. I'm not saying you are wrong, but show me you are not just smoking crack.

[SlowJet]

I was assuming that a 4GB machine would be used for multiple users and server applications.

No, a desktop would be hard pressed to use 4GB by 1 user and with a tempfs would never space much.

But seriously, if a GB or 8 of disk space is such a big deal in your computer environment, you are probably trying to run a modern OS on too little of hardware.

I don't see allocating 2 GB of swap space on an 80 to 500 GB drive as concern in any way shape or form except for your own personal restrictions between your ears and a desire to be right, express your ego, or just to be a control freak.

Smoke that, :)

SJ

[JN4OldSchool]

I don't see allocating 2 GB of swap space on an 80 to 500 GB drive as concern in any way shape or form except for your own personal restrictions between your ears and a desire to be right, express your ego, or just to be a control freak.

I really dont know what I have done to you to cause this intense dislike...nor do I really care. I reckon I am intelligent enough to get by, I really have no desire to be right or wrong, I am probably the most humble person you are likely to encounter in this forum and I couldnt care less what anyone else does so I dont see how I am controling either. I think the majority of people in this forum will agree that I will be the first to admit when I am wrong and that I am really not here to prove anything. I just like to pass the time, BS with my friends and if I can be of help to someone it is my pleasure. I work in the construction trades, I am not a programmer of any sort and computers are strictly a hobby for me. Once again, I have nothing to prove.

If you are running 1GB of RAM or over on a home desktop then it is MHO that anything over 1GB swap is wasted space. You are correct that if I have 400GB worth of drive then I will hardly miss even 10GB. But why be stupid about it?