UMA Frame Buffer Size 256 or 512 MB in a 32 bit with 4 GB RAM setup?

[sling-shot]

I have noticed an entry regarding UMA Frame Buffer Size in the BIOS of my AMD E450 based notebook. It came with 2 GB RAM and Windows 7 Home Basic 64 bit installed. The default value set for this is 256 MB.
However I have an option there to change it to 512 MB.

I have now changed the RAM stick to a 4 GB one.

As my main installation is 32 bit PCLinuxOS KDE, I find that the whole 4 GB is not getting used. If I increase the frame buffer to 512 MB, will it eat away from the approx 3 GB of usable RAM itself, or will it be a block above the one accessible to the OS?

[muungwana]

you should use kernels with ".pae" extension with any 32 bit kernels if your system has RAM greater the 3.5GB

[sling-shot]

Thanks for that suggestion. For reasons of my own I will stick with the existing .bfs kernel for the time being.

I got curious after having been forced to go check the BIOS for some unrelated reason today.

So, back to the topic. Do you know anything about this UMA Buffer Size? Particularly I want to know in this particular situation will it eat away the usable RAM or occupy that un-addressable space above 3.2 GB (for a regular 32 bit kernel)?

NOTE : Many of my questions will be aimed towards acquiring knowledge, not necessarily for implementation right now. I know some other day this knowledge will come handy.

[T6]

we talked about this on a post maybe one year ago(can't find it)

can't remember exactly what was the answer, if i remember correctly it only uses the ram detected by the kernel

sometimes this depends not on the os, in the bios that uses certain size when it sees certain amount of ram

how much ram do you have and how much ram do you see when you open konsole and write top?

[muungwana]

No,i do not know anything about it.

We can speculate and talk in theories of what could or should and you could do the test.

Set it to 512MB, power up and check available memory.
Set it to 256MB,power up and check available memory.

Post if there is any difference and the collective wisdom of the forum will go up by a point or two

[sling-shot]

OK. I am back with the results.

Here is the free output for UMA Frame Buffer size 256 MB :

Code: [Select]

             total       used       free     shared    buffers     cached
Mem:       2850856    2292760     558096          0     617052    1263688
-/+ buffers/cache:     412020    2438836
Swap:      3477500          0    3477500

Here is the corresponding output for 512 MB :

Code: [Select]

             total       used       free     shared    buffers     cached
Mem:       2590652     758512    1832140          0       8632     410080
-/+ buffers/cache:     339800    2250852
Swap:      3477500          0    3477500

It looks like I lose some memory from usable portion itself.

ASIDE : Why does the used memory approach available memory? Or am I reading this output wrong?

[T6]

then it seems that it only uses memory that system see, my memory is not that bad after all 

so you are indeed "wasting" around 1 gb of ram, perhaps you could try a bfs.pae kernel and see how it responds

"Why does the used memory approach available memory?"

linux uses ram very different, i asked this question and had this replies, hope it helps you

http://www.pclinuxos.com/forum/index.php/topic,96403.0.html

[Just17]

A little light reading

http://www.techarp.com/showfreebog.aspx?lang=0&bogno=245

[sling-shot]

Thanks. It indeed explains things.

Although, I have lost some RAM by setting this to 512 MB, it seems to have improved HD video playback by VLC in Windows. Looks lot smoother now.

I have a 1366x768 monitor for my AMD E450 notebook. Theoretically, will it then become a waste to allot 512 MB in this case?

I have also switched to the .pae.bfs kernel. Not seeing any problems. Using all available memory now.

[T6]

waste?  it was being wasted before and is just 256 mbs

the resolution is not big but if you load games or lots of things using 3d you won't see it as a waste, in video cards more is better

[sling-shot]

Output of command "free" now with .pae.bfs kernel:

Code: [Select]

             total       used       free     shared    buffers     cached
Mem:       3626816    1001280    2625536          0      38604     458064
-/+ buffers/cache:     504612    3122204
Swap:      3477500          0    3477500