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#1 2009-01-24 21:31:28

userlander
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Registered: 2008-08-23
Posts: 413

Arch only seeing 3GB of memory out of 4GB!

Just upgraded to two 2GB sticks of ram, but arch is only seeing 3GB total. Does anyone know why this is? thx

 # free -m
             total       used       free     shared    buffers     cached
Mem:          3041        969       2071          0         13        270
-/+ buffers/cache:        685       2355
Swap:         1004          0       1004

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#2 2009-01-24 21:35:27

tsv
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From: UK
Registered: 2008-12-03
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Re: Arch only seeing 3GB of memory out of 4GB!

Are you a 32-bit user? If so you'll probably need to recompile your kernel or move over to 64-bit.

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#3 2009-01-24 22:39:54

userlander
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Registered: 2008-08-23
Posts: 413

Re: Arch only seeing 3GB of memory out of 4GB!

d'oh! you're right. for some reason I thought 32-bit had support for 4GB. thanks

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#4 2009-01-25 01:33:52

Ranguvar
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From: Our collective subconscious
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Re: Arch only seeing 3GB of memory out of 4GB!

Many people have that assumption... it's not quite right. See, 32-bit OSen without PAE have a 4GB address range. This is taken up by RAM, videocard RAM, other devices, etc. So, it varies. Some people see 3GB out of 4GB, some see 3.5GB... etc.

Last edited by Ranguvar (2009-01-25 01:34:08)

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#5 2009-01-25 13:56:36

R00KIE
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From: Between a computer and a chair
Registered: 2008-09-14
Posts: 2,964

Re: Arch only seeing 3GB of memory out of 4GB!

I have the same "issue" but I have decided to move to Arch64 when I have the time. As much as I like trying new stuff and recompiling my own kernel and programs, having everything up to date and working with a simple pacman -Syu is a very good thing as I don't have as much free time as I would like to have. Maybe you could consider moving to Arch64 as well, so far from my tests with Arch64 everything works as expected no problems whatsoever, if it works in Arch32 it sure will work in Arch64.


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#6 2009-01-26 05:06:51

userlander
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Registered: 2008-08-23
Posts: 413

Re: Arch only seeing 3GB of memory out of 4GB!

Ranguvar wrote:

Many people have that assumption... it's not quite right. See, 32-bit OSen without PAE have a 4GB address range. This is taken up by RAM, videocard RAM, other devices, etc. So, it varies. Some people see 3GB out of 4GB, some see 3.5GB... etc.

that explains it, thanks. I remember when I used to compile my own kernels on slackware seeing the highmem option where you could select 4GB, so I just assumed that support was there since then.

It seems like it would make sense for Arch to have an alternate kernel with PAE for those who have 4GB and don't want to reinstall for 64-bit, doesn't it? Everywhere I go it seems like more and more people are going to 4GB minimum, and often even 8GB or more.

R00KIE wrote:

I have the same "issue" but I have decided to move to Arch64 when I have the time. As much as I like trying new stuff and recompiling my own kernel and programs, having everything up to date and working with a simple pacman -Syu is a very good thing as I don't have as much free time as I would like to have. Maybe you could consider moving to Arch64 as well, so far from my tests with Arch64 everything works as expected no problems whatsoever, if it works in Arch32 it sure will work in Arch64.

I'm like you -- After compiling all my own kernels for months and actually years by now (still back at 2.4.x even!) I really like the convenience of just using the stock distro package. I don't mind doing ABS package builds here and there, but if wanted to compile my own kernel and major packages all the time I would just use slackware.

I had 64 installed on a testing partition on my A64 system before this one. It seemed to work just as well as 32, but my main install was the 32-bit so I didn't actually use 64 as much as I thought I was going to. Then one time after not booting into it for a couple months, it choked on an update and I just wiped it.

I had so many problems with flash on my last system, though (and now open source ati drivers on this new one) that I am wary of going to 64 even though I think flash is supposedly okay by now. But I think there might be problems with catalyst at this point, so I don't want to risk it. 3GB is fine for me now anyway, and then it's also nice to know I have a "built-in" upgrade ready to go when I need it just by recompiling the kernel (or upgrading). smile

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#7 2009-01-26 09:54:28

R00KIE
Forum Moderator
From: Between a computer and a chair
Registered: 2008-09-14
Posts: 2,964

Re: Arch only seeing 3GB of memory out of 4GB!

Until I messed up with a custom kernel on my Arch64 and blew it to kingdom come tongue everything was working great, flash, catalyst, OSS tongue, skype wine, no problems whatsoever .... well besides the little annoyance of getting only 3950MB out of my 4G (Arch32 with support for 64GB can get me 4050MB .... just 100MB more I know but still ... they are mine .... my precious 100MB tongue tongue ).
Anyway ... little rant aside, I guess its pretty safe to move to 64bit these days no major problems just because its a 64bit version anymore, if there's trouble usually there is trouble for both 64bit and 32bit versions.


R00KIE
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#8 2009-01-26 11:11:25

Devastator
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From: Poland
Registered: 2008-05-27
Posts: 179

Re: Arch only seeing 3GB of memory out of 4GB!

And how about the performance on 64bit system? I used to have Arch64 on my laptop (Intel Core2 Duo - Santa Rosa architecture), though the 32 version seems to run somewhat... faster. It might be caused by the processor itself, but it was wierd for me...

Did anyone have similiar experience? Or perhaps I just screwed up something? wink


Some applications are WYSIWYG, and some are WYSIWTF.

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#9 2009-01-26 13:41:23

userlander
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Registered: 2008-08-23
Posts: 413

Re: Arch only seeing 3GB of memory out of 4GB!

Devastator wrote:

And how about the performance on 64bit system? I used to have Arch64 on my laptop (Intel Core2 Duo - Santa Rosa architecture), though the 32 version seems to run somewhat... faster. It might be caused by the processor itself, but it was wierd for me...

Did anyone have similiar experience? Or perhaps I just screwed up something? wink

The benchmarks I've seen show that 64-bit supposedly is faster for most things by now, at least on multi-core CPUs. My own subjective experience was that 32-bit was faster in that it felt "snappier," but the difference was so minor that I couldn't be sure I wasn't just imagining it. Otherwise, I didn't really use 64-bit intensively enough to get a good sense of how it did at more demanding tasks like video encoding.

Here's a pretty interesting benchmark review of 32 vs. 64 on fedora:

http://bingouv.blogspot.com/2008/08/des … son32.html

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#10 2009-01-26 15:57:02

Ranguvar
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From: Our collective subconscious
Registered: 2008-08-12
Posts: 2,515
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Re: Arch only seeing 3GB of memory out of 4GB!

32bit vs 64bit is discussed here
http://bbs.archlinux.org/viewtopic.php?id=56793
and here
http://bbs.archlinux.org/viewtopic.php?id=62656

My advice here: http://bbs.archlinux.org/viewtopic.php? … 99#p452499

Please don't bring it up for the nine thousandth time tongue


EDIT: Woah... looks like my 10% estimate was dead-on, according to Fedora... yikes

Last edited by Ranguvar (2009-01-26 15:58:11)

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#11 2009-01-26 16:09:45

Devastator
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From: Poland
Registered: 2008-05-27
Posts: 179

Re: Arch only seeing 3GB of memory out of 4GB!

Yup, I have found two of these threads later... sorry for the mess smile.


Some applications are WYSIWYG, and some are WYSIWTF.

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