ram memory use in fedora 15

[Moore]

Hi,.
Can some one explain the following anomaly :

When I look for memory information on the laptop I get the following:

sudo dmidecode --type 17

# dmidecode 2.11
SMBIOS 2.6 present.

Handle 0x0013, DMI type 17, 28 bytes
Memory Device
	Array Handle: 0x0011
	Error Information Handle: Not Provided
	Total Width: 64 bits
	Data Width: 64 bits
	Size: 2048 MB
	Form Factor: SODIMM
	Set: None
	Locator: DIMM0
	Bank Locator: BANK 0
	Type: DDR3
	Type Detail: Synchronous
	Speed: 1067 MHz
	Manufacturer: 80CE
	Serial Number: 86BB7A0A
	Asset Tag: Unknown
	Part Number: M471B5673EH1-CF8  
	Rank: Unknown

Handle 0x0016, DMI type 17, 28 bytes
Memory Device
	Array Handle: 0x0011
	Error Information Handle: Not Provided
	Total Width: 64 bits
	Data Width: 64 bits
	Size: 2048 MB
	Form Factor: SODIMM
	Set: None
	Locator: DIMM2
	Bank Locator: BANK 2
	Type: DDR3
	Type Detail: Synchronous
	Speed: 1067 MHz
	Manufacturer: 80CE
	Serial Number: 86BB7A54
	Asset Tag: Unknown
	Part Number: M471B5673EH1-CF8  
	Rank: Unknown

So as I'd expect, it is 4G of RAM.


However when I do a top, it displays that only ~3G is available.

top - 12:07:46 up 2:32, 10 users, load average: 0.19, 0.18, 0.40
Tasks: 190 total, 1 running, 189 sleeping, 0 stopped, 0 zombie
Cpu(s): 2.7%us, 0.4%sy, 0.0%ni, 96.8%id, 0.0%wa, 0.0%hi, 0.1%si, 0.0
Mem: 3083312k total, 2919900k used, 163412k free, 214396k buffers
Swap: 5177340k total, 112k used, 5177228k free, 1940580k cached


Why is this the case?
I think on the previous version of fedora I had (fc 13), it was seeing the 4G.

thanks.

[diamond_ramsey]

Off-hand, do you know your kernel version?

- try a post of your uname -airvn output

[Moore]

>uname -a
Linux madmax 2.6.38.8-35.fc15.i686 #1 SMP Wed Jul 6 14:46:26 UTC 2011 i686 i686 i386 GNU/Linux

[diamond_ramsey]

Originally Posted by Moore

>uname -a
Linux madmax 2.6.38.8-35.fc15.i686 #1 SMP Wed Jul 6 14:46:26 UTC 2011 i686 i686 i386 GNU/Linux

Looks like you have a Fedora 15, 32-bit installed system. Highly likely you will need to try a PAE kernel or a 64-bit install. Depends in your system and your needs. Is your laptop 64-bit?

Hope this helps.

[AdamW]

It's entirely normal for a non-PAE i686 kernel to do this. For some interesting info on why, see http://www.dansdata.com/askdan00015.htm . Dan mentions 'Windows' quite a lot but actually, most of the issues there affect any 32-bit, non-PAE OS.

If you installed the 64-bit version of Fedora you'd have all 4GB of RAM available, though 64-bit apps use more RAM than 32-bit apps; around 33% on average. So what you'd gain on the swings you'd lose on the roundabouts.

You could also install a 32-bit PAE kernel; you'd then have all 4GB available and no increased usage of RAM by apps, but you'd have a small general performance hit (I think it's 1-5% or so).

Or if you never actually get above 3GB of RAM used, you could just keep using the kernel you have.

(PAE is a sort of hack which allows 32-bit kernels to address RAM beyond the first 4GB of address space, but with a small performance hit).

[Moore]

Thanks for the replies and info. Yes it is 32 bit OS on 64 bit system. With 32 bit I thought that it should in theory access all 4G. However I do remember some previous kernels I had having a pae tag. Thanks.