3GB limit on 32 bit OS

Khannie

So....I have a box in work with 4G, and it reports 3G of memory available (ubuntu x86 feisty). Apparently the kernel keeps a whopping 1G for itself. Does the kernel really need this much? Or is it just being greedy?

I saw a thread here which shows how to reduce the amount of ram that the kernel needs (and I'm not averse to carrying out this hack), but ultimately I'm after maximum performance. I will not need > 3GB for any individual process, but I bought the extra ram to primarily help with the kernel level caching that linux does.

Thoughts? Suggestions?

AndrewMc

A quick search suggests 32-bit Linux can ordinarily only recognise up to about 3GB RAM. You'll need to re-compile the kernel with the CONFIG_HIGHMEM64G option, at the risk of slower memory accesses: http://ubuntuforums.org/showthread.php?t=458147

I presume the CPU isn't 64-bit?

leeroybrown

Ubuntu comes with a 'BigIron Server' kernel that has CONFIG_HIGHMEM64G enabled by default. You could try that on the machine.

Khannie

AndrewMc wrote:

A quick search suggests 32-bit Linux can ordinarily only recognise up to about 3GB RAM. You'll need to re-compile the kernel with the CONFIG_HIGHMEM64G option, at the risk of slower memory accesses: http://ubuntuforums.org/showthread.php?t=458147

leeroybrown wrote:

Ubuntu comes with a 'BigIron Server' kernel that has CONFIG_HIGHMEM64G enabled by default. You could try that on the machine.

I think these are basically both the same suggestion....Apparantly there aren't modules for the nvidia drivers for this kernel. Compiling things from source on ubuntu is horrible. Also using the PAE (to access > 2^32 bits) costs about 3-6% in performance. :eek:

Somewhat starting to regret not installing gentoo now.

Anyone any suggestion on whether machine performance would be better if I hacked say 512M (or possibly less) reserved for the kernel?

AndrewMc wrote:

I presume the CPU isn't 64-bit?

'tis yeah. It's an E6700. My understanding is that 64bit linux is still a bit lacking in software support v's 32bit. I'm not saying it's not stable or anything. Just that it's not quite as lovely as 32bit yet, or that it's hacky for things like flash support. We all need a youtube lol at lunchtime.

On an unrelated topic: Is it possible to apt-get an upgrade to 64bit ubuntu?

AndrewMc

Khannie wrote:

Compiling things from source on ubuntu is horrible.

I quite like the way it works . Compiling a kernel shouldn't be too much hassle: https://help.ubuntu.com/community/Kernel/Compile

Khannie wrote:

Anyone any suggestion on whether machine performance would be better if I hacked say 512M (or possibly less) reserved for the kernel?

How do you mean?

Khannie wrote:

It's an E6700. My understanding is that 64bit linux is still a bit lacking in software support v's 32bit. I'm not saying it's not stable or anything. Just that it's not quite as lovely as 32bit yet, or that it's hacky for things like flash support. We all need a youtube lol at lunchtime.

3rd party software that's 32-bit only is the only irritating bit. I haven't checked lately, but 64-bit Firefox can't use 32-bit plugins. You can either install 32-bit Firefox, or use a different browser — I switch to 32-bit Opera for the rare occasions I need flash. Things like ndiswrapper don't always work so well, but fortunately I don't need it anyway.

I can't think of any open-source software that doesn't work with it. You also mentioned the nvidia drivers. I'm using the (commercial) ones on two different 64-bit systems with no trouble.

Khannie wrote:

On an unrelated topic: Is it possible to apt-get an upgrade to 64bit ubuntu?

No, I don't think so. Sorry!

Khannie

Thanks for the reply.

AndrewMc wrote:

I quite like the way it works .

The gentoo way is much lovlier for compiling from source. Everything's already there. Of course gentoo has its disadvantages too.

AndrewMc wrote:

How do you mean?

The missing 1G is reserved by the kernel. It's possible to reduce that 1G to (for example) 512M. What I'd like to know is whether this will positively or negatively affect performance.

AndrewMc wrote:

3rd party software that's 32-bit only is the only irritating bit. I haven't checked lately, but 64-bit Firefox can't use 32-bit plugins. You can either install 32-bit Firefox, or use a different browser — I switch to 32-bit Opera for the rare occasions I need flash. Things like ndiswrapper don't always work so well, but fortunately I don't need it anyway.

I can't think of any open-source software that doesn't work with it. You also mentioned the nvidia drivers. I'm using the (commercial) ones on two different 64-bit systems with no trouble.

Nice one. Thanks. I just have everything set up for dev now, so I'll probably stick with 32bit for now at least.

Nietzschean

i dunno i'd just make the swap to 64bit, i've a few boxes setup for dev in 64bit linux with no major problems, you can build/run 32bit apps if you wish on it and link against the 32bit libraries....

and its linux, setup shuoldn't take too long, one of the wonderfull thigns about it , grab /etc and /home and its about 95% of the work gone in my experence?


and wrt kernel compiling, i'm not an ubuntu user but i have extensively used debian which its based on compiling kernels and the like, its actually amazingly trivial to do, there is a package you can get whose name eludes me currently that basically does most of the work producing you a nice .deb file to install....

leeroybrown

Khannie wrote:

We all need a youtube lol at lunchtime.

A slight aside. The Gnash project is coming along nicely. I wouldn't be surprised if a CVS or snapshot build of it would work with youtube on x86_64.