Linux supports only certain amounts of RAM?

[Kamisama]

OS: Debian Lenny

So, I was on a website that discussed how the kernel only supports certain amounts of RAM depending on the box's architecture. I lost the website. I looked at "free" and noticed it doesn't see all of my RAM, which is 2GB. It seems like it only notices...

906492/1024=885MB RAM.

-----------------------------------------------------------------------------------------------------------
total used free shared buffers cached
Mem: 906492 744740 161752 0 32276 349304
-/+ buffers/cache: 363160 543332
Swap: 0 0 0
------------------------------------------------------------------------------------------------------------

Yeah, I don't like that.

There was also something in /proc I looked at. Either way, the computer doesn't see the full 2GB RAM. I didn't notice this until about a few weeks ago. I also noticed my other box with 4GB isn't noticing all of its RAM. MAYBE all of the RAM is being used upon consumption of the already known RAM, but I wouldn't know that for sure.

Anyway to get all of the RAM recognized.
This is a kernel issue, right?

# uname -a

Linux characters 2.6.25-2-486 #1 Fri Jul 18 17:03:35 UTC 2008 i686 GNU/Linux

[Prometheum]

Are you sure BLOCKSIZE isn't set to something weird? Try free -m or free -g to see it in a more human-readable form.

i'm curious, how are you checking your ram. i want to check it the same way you do.

[Prometheum]

Originally Posted by hoaxe

i'm curious, how are you checking your ram. i want to check it the same way you do.

He's using the program free(1).

[Kamisama]

computer@linux:~$ dmesg |grep -i memory
[ 1.099677] Freeing unused kernel memory: 320k freed

computer@linux:~$ cat /proc/meminfo
MemTotal: 906492 kB
MemFree: 247324 kB
Buffers: 60220 kB
Cached: 320176 kB
SwapCached: 0 kB
Active: 389668 kB
Inactive: 232132 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 2116 kB
Writeback: 0 kB
AnonPages: 241424 kB
Mapped: 59268 kB
Slab: 18560 kB
SReclaimable: 9744 kB
SUnreclaim: 8816 kB
PageTables: 1932 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
CommitLimit: 453244 kB
Committed_AS: 518768 kB
VmallocTotal: 122564 kB
VmallocUsed: 46952 kB
VmallocChunk: 70844 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 4096 kB

computer@linux:~$ free
total used free shared buffers cached
Mem: 906492 659136 247356 0 60220 320176
-/+ buffers/cache: 278740 627752
Swap: 0 0 0

computer@linux:~$ free -m
total used free shared buffers cached
Mem: 885 643 241 0 58 312
-/+ buffers/cache: 272 613
Swap: 0 0 0

computer@linux:~$ free -g
total used free shared buffers cached
Mem: 0 0 0 0 0 0
-/+ buffers/cache: 0 0
Swap: 0 0 0

[Prometheum]

This is happening on both boxes? Does the RAM show up in BIOS and in memtest86?

The box with 4 gigs almost certainly isn't a hardware/software issue. You can't expect to see all 4 gigs on most 32-bit systems because you only get 32-bits of addressable virtual memory, only some of which will map to RAM. Actually chip support is commonly 36-bit now-a-days even when running in 32-bit mode and I think you can compile a kernel with support for PAE and see all 4 gigs, but most kernels don't compile with this by default to keep support for legacy processors (really fucking stupid...legacy meaning before pentium pros).

Your other box most likely has fucked up RAM or slots or something.

[Kamisama]

The answer was to use a different x86 kernel.


Kernel 2.6.25-2-486 didn't allow me to see 2GB RAM.
However, Linux kernel 2.6.25-2-686 allowed me to see ~2GB RAM.
Also, there is a noticeable difference in performance with some programs, such as flight gear.
Yeah, I used synaptic to read the description of the different kernels available.
The desc riptions tipped me off as to what to use.

But now we know, and that's half the battle.
So, if any of you come across a problem like this, think about what kernel type to use.

$ free
             total       used       free     shared    buffers     cached
Mem:       2010352    1647912     362440          0     225148    1008116
-/+ buffers/cache:     414648    1595704
Swap:            0          0          0