2008 macbook - 8GB RAM installed but 4GB available

safeness

Hello,

I'm running a full 64-bit system with 8GB physical RAM installed but only 4GB are usable. I looked around in the kernel menuconfig (via genkernel) but didn't see anything about HIMEM limits or anything like that.

In MacOS all 8GB are usable but I just can't find anything about enabling the last 4GB in Gentoo.

Any ideas?

Thanks in advance!

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

Did you possibly set a maximum memory limit in the kernel configuration?

safeness · Posted: Thu Aug 20, 2015 4:29 am Post subject:

That's the confusing thing, I went through all the options in menuconfig and didn't see an option for that anywhere.

Here's my uname info:

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

There are a few possibilities:

- Actual memory limit in Boot Camp (I assume you are using BIOS emulation on your Mac). I suggest updating Boot Camp on your Mac to the latest version possible just in case (really you should update your OS X version to the latest possible for this).
- You have a mem= boot flag in GRUB/LILO/etc
- You have a memory limit set in the kernel configuration

What I have seen is that the graphics card will reserve memory from the main RAM, in particular the Intel ones. But maybe on older models where there isn't a hybrid GPU setup all GPUs will reserve memory. But I have extreme doubts the video card will take 4 GiB for itself.

You should post your kernel configuration, and your boot log, /var/log/dmesg. In the first few seconds of the log you will see how the memory is discovered. Mine:

safeness · Posted: Sat Aug 22, 2015 4:14 pm Post subject:

Here's my dmesg:

safeness · Posted: Sat Aug 22, 2015 4:21 pm Post subject:

Oh, I should note that I'm not using bootcamp to dual boot I'm just using refind + grub2. The latest MacOS I can update to is 10.7 as well. Here's another bit from dmesg that seemed relevant:

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

The range the kernel is seeing is only about 5.36 GiB and some memory is definitely taken by your GPU (however you gave only one line which indicates 16 MiB was taken, but I would imagine more was taken, perhaps ~1.36 GiB). I have seen reports of people seeing half the memory in Boot Camp (or otherwise known as BIOS emulation) on Windows. You could try booting a true EFI kernel (either with EFI-based GRUB or EFI stub) with rEFInd and see if that gets the full amount of memory. Right now you are using BIOS emulation with a hybrid disk.

Otherwise, not sure what is causing this.

safeness · Posted: Sun Aug 23, 2015 7:41 pm Post subject:

Here's the full output of dmesg if that helps. I tried to trim it down before but might have done too much.

http://pastebin.com/92J77Qfz

Oh, also I have EFI enabled in GRUB and in the kernel.

USE flags for grub2:

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

If you're certain you are getting > 4 GiB on OS X, then you are going above the supported limit.

http://www.everymac.com/actual-maximum-mac-ram/actual-maximum-macbook-ram-capacity.html

That does not mean anything inherently bad, but it could be that Apple enforces the limit in Boot Camp and/or they do not expect people to use 64-bit operating systems in Boot Camp. This would explain the limit.

On a Mac: https://discussions.apple.com/thread/4046267?start=0&tstart=0 and http://www.rodsbooks.com/gdisk/repairing.html

I would still try a EFI (non-hybrid partition scheme) boot. You need to undo the hybrid partition (which will effectively delete it), and install Gentoo on a newly partition on the GPT partition. Since you would be booting Gentoo in MBR mode to install it, you cannot use the Gentoo disc. You need to use something like Ubuntu or some other OS that officially supports EFI booting fully. If you boot with the Ubuntu USB or CD in, and hold C while booting, you should get 2 or 3 options: OS X, Ubuntu, and rEFInd. Pick Ubuntu with 'Try out' option or similar and proceed with an install. Also in Ubuntu you can run Gparted and create the new partition(s) for Gentoo (and you must ignore warnings about not having an MBR). Once you are ready to install GRUB2, you need to ensure you are running with the correct options and not installing a MBR-based GRUB.

Example:

safeness · Posted: Mon Aug 24, 2015 12:45 am Post subject:

That's curious about the hybrid partition scheme. I wasn't aware of anything like that. Here's what I have:

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

From that layout it seems you do not have a hybrid MBR. You should be able to create an EFI entry for your EFI-based GRUB2 or your own Linux EFI stub kernel if you decide to do that. Without enabling FileVault this is relatively easy. And if you want to use rEFInd then all you need to do is add a stanza to the configuration with the correct path to the binary.

Tatsh · Apprentice Joined: 22 Jul 2007 Posts: 187

As for the original issue, it looks like it is not what I suspected: Boot Camp. You do not appear to be using any part of Boot Camp although your dmesg output is kind of weird to me. Not sure what the issue is here. Reading the ranges from the 'BIOS' output lines is not exactly correct. This is not always going to be the amount of memory you actually have.

Do you boot raw or do you use an initrd? If you use an initrd then there would be a slight difference in dmesg logs, and it would be better to get that log instead of the post-switch one.