4gb memory shows up as 3.2?

Message

mlybarger · Post by **mlybarger** » Fri Aug 25, 2006 11:38 pm

i've got an amd opteron machine, with an opteron built kernel. it has 4 1gb memory sticks of corsair memory, but the memory is showing up as 3237M?

i've heard of a highmem that some set, but that's not available in my kernel .config (dont't see it in make menuconfig). i also set mem=4096M to the kernel in the /boot/grub/grub.conf file. ???

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mark@expresso ~ $ free -m
             total       used       free     shared    buffers     cached
Mem:          3237        295       2942          0         12        136
-/+ buffers/cache:        145       3092
Swap:         1913          0       1913
mark@expresso ~ $ cat /proc/meminfo
MemTotal:      3315656 kB
MemFree:       1743696 kB
Buffers:        442720 kB
Cached:         170232 kB
SwapCached:          0 kB
Active:         550016 kB
Inactive:       187984 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:      3315656 kB
LowFree:       1743696 kB
SwapTotal:     1959888 kB
SwapFree:      1959888 kB
Dirty:              28 kB
Writeback:           0 kB
Mapped:         193668 kB
Slab:           799304 kB
CommitLimit:   3617716 kB
Committed_AS:   273632 kB
PageTables:       6312 kB
VmallocTotal: 34359738367 kB
VmallocUsed:     16268 kB
VmallocChunk: 34359720955 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

Crenshaw · Post by **Crenshaw** » Sat Aug 26, 2006 12:41 am

I guess you're missing option in kernel to support more memory.

It's here listing 3.7:
http://www.gentoo.org/doc/en/kernel-config.xml

region-g · Post by **region-g** » Sat Aug 26, 2006 12:46 am

Hello there ...

Try to check Processor type and features --->
High Memory Support (4GB) --->

allexey1985 · Post by **allexey1985** » Sat Aug 26, 2006 8:08 am

Maybe you need to enable Processor type and features->K8 GART IOMMU support (GART_IOMMU)

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Support for hardware IOMMU in AMD's Opteron/Athlon64 Processors
and for the bounce buffering software IOMMU.
Needed to run systems with more than 3GB of memory properly with
32-bit PCI devices that do not support DAC (Double Address Cycle).
The IOMMU can be turned off at runtime with the iommu=off parameter.
Normally the kernel will take the right choice by itself.
This option includes a driver for the AMD Opteron/Athlon64 IOMMU
northbridge and a software emulation used on other systems without
hardware IOMMU. If unsure, say Y.

And enable IOMMU in BIOS.

mlybarger · Post by **mlybarger** » Sat Aug 26, 2006 3:32 pm

allexey1985 wrote:Maybe you need to enable Processor type and features->K8 GART IOMMU support (GART_IOMMU)
And enable IOMMU in BIOS.

I have IOMMU enabled in kernel, but it's not available in the bios?

dweigert · Post by **dweigert** » Sun Aug 27, 2006 3:11 am

Look for a bios option to move the PCI address space to the end of memory, rather than where it is.

kernelcowboy · Post by **kernelcowboy** » Fri Sep 15, 2006 10:23 am

What motherboard do you have?

I have a Gigabyte GA-LK8NS Ultra-939; I've considering getting
more RAM and was flipping through the docs to find this

Due to standard PC architecture, a certain amount of memory
is reserved for system usage and therefore the actual memory size is
less than the stated amount. For example, 4 GB of memory size will
instead be shown as 3.xxGB memory during system startup.

I'm not sure I 100% understand that. But, it does look curious.

I wonder what you BIO is stating you have for memory?

Mad Merlin · Post by **Mad Merlin** » Fri Sep 15, 2006 2:37 pm

Is this a 32 bit or a 64 bit install?

kernelcowboy · Post by **kernelcowboy** » Fri Sep 15, 2006 7:56 pm

Mad Merlin wrote:Is this a 32 bit or a 64 bit install?

Yes, I think. What do you mean exactly?
(Nevermind, Sorry just realized you're not asking me.)

Ast0r · Post by **Ast0r** » Mon Sep 18, 2006 7:15 pm

I am having the same problem. I have a machine with 4x1GB (Corsair) and it was able to use all 4GB until I installed kernel-2.6.17. Now there is only 3370232k.

Here is the relevant section of the kernel config (pulled via /proc/config.gz)

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# CONFIG_NOHIGHMEM is not set
CONFIG_HIGHMEM4G=y
# CONFIG_HIGHMEM64G is not set
CONFIG_PAGE_OFFSET=0xC0000000
CONFIG_HIGHMEM=y
CONFIG_ARCH_FLATMEM_ENABLE=y
CONFIG_ARCH_SPARSEMEM_ENABLE=y
CONFIG_ARCH_SELECT_MEMORY_MODEL=y
CONFIG_SELECT_MEMORY_MODEL=y
CONFIG_FLATMEM_MANUAL=y

What the hell happened? Why can't I use all 4GB anymore.

fangorn · Post by **fangorn** » Fri Sep 22, 2006 6:00 am

What you guys need is to enable remapping memory around the address space reserved by the PCI bus.

As PCI is only 32bit it can only address 4 GB of memory. So everything it has to handle is mapped to the area under 4GB. If you put in more than 3 GB you have to activate in BIOS something like "Hardware Memory Hole" (my board has "Software Memory Hole" too), which moves the logical adreesses blocked by the PCI bus to addresses over 4GB.

But be carefull, as this option made my onboard NIC completely useless. I suspect some problems in the kernel driver.

96140 · Post by **96140** » Fri Sep 22, 2006 8:16 am

Weird. So, is anyone able to use kernel 2.6.17 with 4GB of memory? Perhaps it's just reporting the available memory incorrectly, but it's actually making use of it. I suppose the only way to test is to start loading a lot of apps.

Oh, and whoever posted that link to the kernel config guide -- that's incorrect. Please re-read the part where it said those steps are for x86 only.

Ast0r · Post by **Ast0r** » Fri Sep 22, 2006 8:32 am

nightmorph wrote:Weird. So, is anyone able to use kernel 2.6.17 with 4GB of memory? Perhaps it's just reporting the available memory incorrectly, but it's actually making use of it. I suppose the only way to test is to start loading a lot of apps.

This is what I was thinking. I will know in about a week (I think ... whenever my new hardware comes in ) when I get a chance to reboot the box in question with a 64GB-enabled kernel.

The machine in question is already running PostgreSQL with about 2GB of (shared) memory allocated. I guess I could try bumping the kernel shared memory max above 3.2 and then try allocating more than 3.2GB in PostgreSQL and see what happens. I have a sneaking suspicion that the kernel won't do this though.

96140 · Post by **96140** » Fri Sep 22, 2006 8:48 am

I suppose you could try rebooting it with just the 64GB kernel option to see if it's a bug in the 4GB code, without waiting for your new hardware.

I checked over at kernel.org's bugzilla for similar problems, but couldn't find anything.

Ast0r · Post by **Ast0r** » Fri Sep 22, 2006 9:06 am

nightmorph wrote:I suppose you could try rebooting it with just the 64GB kernel option to see if it's a bug in the 4GB code, without waiting for your new hardware.

I checked over at kernel.org's bugzilla for similar problems, but couldn't find anything.

I suppose I could, but I don't want to risk the machine not booting for one reason or another. I like to be present when I reboot the machines with a siginificantly different kernel. When the hardware comes in I have to go down to the datacenter and install it anyway, so I would rather just make one trip and only have one set of downtime. I will post back here when I know.