Recently installed arch system doesn't show all my RAM memory.

iseedeadpeople · 2012-06-05 12:20:38

Hello!

I'm having a problem, archlinux isn't identifying all my memory. I'm using a Lenovo Thinkpad W500 with 4GB ram. Before arch I had Lubuntu and it showed correctly my 4GB of RAM. I did some research and found that Linux uses your memory for disk cashing, it seems that this is usually a source of confusion for newbies like myself, but I think my problem is not related.

Here is some useful information:

Output of free -t from archlinux:

             total       used       free     shared    buffers     cached
Mem:       2545944     696732    1849212          0      22620     277104
-/+ buffers/cache:     397008    2148936
Swap:       975868          0     975868
Total:     3521812     696732    2825080

Output of free -t from lubuntu:

             total       used       free     shared    buffers     cached
Mem:       4008660     738232    3270428          0      85884     450348
-/+ buffers/cache:     202000    3806660
Swap:            0          0          0
Total:     4008660     738232    3270428

Both arch and lubuntu are on the same disk. I have lubuntu as a backup.

Thanks in advance!

Awebb · 2012-06-05 12:41:01

64bit lubuntu vs. 32bit Arch?

Edit:
Maybe lubuntu uses a bigmem kernel. If I am not mistaken, Debian made the bigmem kernel the default 32bit kernel a year ago (I might be wrong on this). Since turds roll down hill and Debian → Ubuntu → Lubuntu, you might have a bigmem kernel. Try 64bit Arch, if your CPU supports it.

Last edited by Awebb (2012-06-05 12:42:54)

iseedeadpeople · 2012-06-05 12:58:48

I see. I will try with 64bit arch then.

However, I find it strange that arch 32bit doesn't support 4GB of RAM by default. After all you can correctly index that amount of memory with a 32bit data bus.

Thank you for your reply Awebb!

Pres · 2012-06-05 13:11:58

It's because with only 4GB of address space, it must assign some of that to other hardware devices.

falconindy · 2012-06-05 13:14:55

You can't even properly support over 1GiB of RAM on 32bit without hacks -- see CONFIG_HIGH_MEMORY. Even with that enabled, the PCI bus will not be able to access memory above the 1GiB mark. Still, because of MMIO, address remapping, and sometimes hardware restrictions, a 32 bit OS generally won't be able to address over 3.2GB. To go beyond this requires PAE, which Ubuntu enables. Arch won't do this (search the bug tracker). Use 64 bit.

alphaniner · 2012-06-05 13:18:16

However, I find it strange that arch 32bit doesn't support 4GB of RAM by default. After all you can correctly index that amount of memory with a 32bit data bus.

I'm beyond my level of incompetence here, but I think it depends on the hardware. I've seen different machines (with 4+GB) running XP which reported different amounts of RAM.

iseedeadpeople · 2012-06-05 14:02:32

falconindy, yes, I think I remember seeing some messages about PAE at boot.

Thank you for your replies guys. It appears that installing 64bit arch is the only sensible choice. Unfortunately I will have to reconfigure my system and reinstall all my apps . Is there any way to avoid this, at least partially?

Edit: I just found some useful wiki entries that answer my previous question, I will leave them here for future reference:

Arch64 wiki
https://wiki.archlinux.org/index.php/Arch64_FAQ

Migrating between architectures without reinstalling
https://wiki.archlinux.org/index.php/Mi … installing

Last edited by iseedeadpeople (2012-06-05 14:09:12)

doug piston · 2012-06-05 14:09:20

This may help.

https://wiki.archlinux.org/index.php/Ar … talling.3F

Edit:

MIssed it by that much. This is what I get for getting coffee in between,

Last edited by doug piston (2012-06-05 14:11:19)

Pres · 2012-06-05 14:18:13

You can back up a list of your installed packages to easily reinstall if the above methods don't work (probably a good idea to generate the list anyways though):
https://wiki.archlinux.org/index.php/Pa … d_packages

iseedeadpeople · 2012-06-05 23:08:01

I just finished installing arch 64bits and my RAM went up by a substantial amount. However, I still don't have as much as I had with Lubuntu . I guess this is because of how Archlinux works?

Output of free -t:

             total       used       free     shared    buffers     cached
Mem:       3945540     786636    3158904          0      21608     305024
-/+ buffers/cache:     460004    3485536
Swap:            0          0          0
Total:     3945540     786636    3158904

Last edited by iseedeadpeople (2012-06-05 23:08:42)

falconindy · 2012-06-05 23:40:11

Because the kernel on lubuntu is not the kernel on ARCH. Reserved memory varies kernel to kernel, version to version. So sure, if you want to say that it's "because of how Archlinux works"... sure... why not...

Arch Linux

#1 2012-06-05 12:20:38

Recently installed arch system doesn't show all my RAM memory.

#2 2012-06-05 12:41:01

Re: Recently installed arch system doesn't show all my RAM memory.

#3 2012-06-05 12:58:48

Re: Recently installed arch system doesn't show all my RAM memory.

#4 2012-06-05 13:11:58

Re: Recently installed arch system doesn't show all my RAM memory.

#5 2012-06-05 13:14:55

Re: Recently installed arch system doesn't show all my RAM memory.

#6 2012-06-05 13:18:16

Re: Recently installed arch system doesn't show all my RAM memory.

#7 2012-06-05 14:02:32

Re: Recently installed arch system doesn't show all my RAM memory.

#8 2012-06-05 14:09:20

Re: Recently installed arch system doesn't show all my RAM memory.

#9 2012-06-05 14:18:13

Re: Recently installed arch system doesn't show all my RAM memory.

#10 2012-06-05 23:08:01

Re: Recently installed arch system doesn't show all my RAM memory.

#11 2012-06-05 23:40:11

Re: Recently installed arch system doesn't show all my RAM memory.

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