8GB RAM Kernel Panic

[losmurfs]

I have a Dell Dimension XPS 400 with 8GB of RAM. If I boot into Windows XP Professional Windows sees 4GB of RAM. If I enter the BIOS it sees 8GB of RAM. If I boot Kubuntu I get a Kernel Panic. If I add add entry to menu.lst in grub:

title Ubuntu 7.10, kernel 2.6.22-14-server (4GB Limit)
root (hd0,4)
kernel /boot/vmlinuz-2.6.22-14-server root=UUID=7eb4293b-aefa-4f13-9e37-dc3afcb088b6 ro quiet splash mem=4000m
initrd /boot/initrd.img-2.6.22-14-server
quiet

(Note the mem=4000m)

It boots just fine but only sees 4GB (or maybe 3.5GB)

So, how do I enable support for 8GB of RAM?

Other distros have -hugemem- images. How do I enable this setting via make menuconfig? Or do I need something like CONFIG_HIGHMEM64G=y for x86_64 SMP kernels? Anyone running (K)ubuntu with over 4GB? Is it a bug in my BIOS or Motherboard/chipset? I even tried the server kernel and still get the same kernel panic.

[dibl]

Re: 8GB RAM Kernel Panic

Did you install 32-bit or 64-bit Kubuntu? I don't think the 32-bit can address more than about 3.8 or 3.9G of RAM.

[Snowhog]

Re: 8GB RAM Kernel Panic

PAE - Physical Address Extension

"The Linux kernel supports PAE starting from 2.6."
"It has full PAE support, enabling access of up to 64 GiB of memory on 32-bit machines."
"A PAE-enabled Linux-kernel won't work on CPUs without PAE."

"In computing, Physical Address Extension (PAE) refers to a feature of x86 and x86-64 processors that allows more than 4 gibibytes (GiB) of physical memory to be used in 32-bit systems, given appropriate operating system support. PAE is provided by Intel Pentium Pro and above CPUs (including all later Pentium-series processors except the 400 MHz bus versions of the Pentium M), as well as by some compatible processors such as Athlon and later models from AMD.

The x86 processor hardware is augmented with additional address lines used to select the additional memory, so physical address size is increased from 32 bits to 36 bits. This increases maximum physical memory size from 4 GiB to 64 GiB. The 32-bit size of virtual address is not changed, so regular application software continues to use instructions with 32-bit addresses and (in a flat memory model) is limited to 4 gibibytes (GiB). The operating system uses page tables to map this 4 GiB address space onto the 64 GiB of total memory, and the map is usually different for each process. In this way the extra memory is useful even though no single regular application can access it all simultaneously."

"Memory

The 32-bit server kernel supports up to 64 GB of memory; the desktop kernel, a mere 4 GB (CONFIG_HIGHMEM64G=y, CONFIG_HIGHMEM4G=y). You'll only see these options in 32-bit kernels because the 32-bit address space is big enough to support only 4 GB without trickery. Or by using the Intel Physical Address Extension (PAE) mode, if you want to get technical. Linux supports PAE, and you also need PAE support in your CPU. Anything newer than a Pentium Pro or AMD K6-3 should be fine. On a 64-bit system you won't see any memory options because it doesn't need hacks to overcome a lack of memory addressing space; you should be fine until your needs exceed 16 exabytes of RAM."

Info above courtesy of our friend Google.

[deviance]

Re: 8GB RAM Kernel Panic

You need to use the 64bit version as stated above.

The global limit for 32bit is 4gb, including Video memory.

Therefore, if you have a 512mb video card, you will only see 3.5gb of system ram.

[losmurfs]

Re: 8GB RAM Kernel Panic

Yes, I am using the 64 bit version of kubuntu 7.10, but I get a kernel panic when I have 8gb installed and don't have mem=4000m. My BIOS sees 8GB. So, by default you are saying if I run 64-bit Kubuntu, the default generic 64-bit kernel allows >4GB?

[losmurfs]

Re: 8GB RAM Kernel Panic

Here's My CPU:

cpuid
eax in eax ebx ecx edx
00000000 00000006 756e6547 6c65746e 49656e69
00000001 00000f64 00020800 0000e4bd bfebfbff
00000002 605b5101 00000000 00000000 007d7040
00000003 00000000 00000000 00000000 00000000
00000004 00000000 00000000 00000000 00000000
00000005 00000040 00000040 00000000 00000000
00000006 00000000 00000000 00000000 00000000
80000000 80000008 00000000 00000000 00000000
80000001 00000000 00000000 00000001 20100800
80000002 20202020 20202020 20202020 6e492020
80000003 286c6574 50202952 69746e65 52286d75
80000004 20442029 20555043 30322e33 007a4847
80000005 00000000 00000000 00000000 00000000
80000006 00000000 00000000 08006040 00000000
80000007 00000000 00000000 00000000 00000000
80000008 00003024 00000000 00000000 00000000

Vendor ID: "GenuineIntel"; CPUID level 6

Intel-specific functions:
Version 00000f64:
Type 0 - Original OEM
Family 15 - Pentium 4
Extended family 0
Model 6 -
Stepping 4
Reserved 0

Extended brand string: " Intel(R) Pentium(R) D CPU 3.20GHz"
CLFLUSH instruction cache line size: 8
Hyper threading siblings: 2

Feature flags bfebfbff:
FPU Floating Point Unit
VME Virtual 8086 Mode Enhancements
DE Debugging Extensions
PSE Page Size Extensions
TSC Time Stamp Counter
MSR Model Specific Registers
PAE Physical Address Extension
MCE Machine Check Exception
CX8 COMPXCHG8B Instruction
APIC On-chip Advanced Programmable Interrupt Controller present and enabled
SEP Fast System Call
MTRR Memory Type Range Registers
PGE PTE Global Flag
MCA Machine Check Architecture
CMOV Conditional Move and Compare Instructions
FGPAT Page Attribute Table
PSE-36 36-bit Page Size Extension
CLFSH CFLUSH instruction
DS Debug store
ACPI Thermal Monitor and Clock Ctrl
MMX MMX instruction set
FXSR Fast FP/MMX Streaming SIMD Extensions save/restore
SSE Streaming SIMD Extensions instruction set
SSE2 SSE2 extensions
SS Self Snoop
HT Hyper Threading
TM Thermal monitor
31 reserved

TLB and cache info:
51: Instruction TLB: 4KB and 2MB or 4MB pages, 128 entries
5b: Data TLB: 4KB and 4MB pages, 64 entries
60: unknown TLB/cache descriptor
40: No 2nd-level cache, or if 2nd-level cache exists, no 3rd-level cache
70: Trace cache: 12K-micro-op, 4-way set assoc
7d: unknown TLB/cache descriptor
Processor serial: 0000-0F64-0000-0000-0000-0000

[dibl]

Re: 8GB RAM Kernel Panic

I can't verify it empirically, because I have only 4GB installed, but I've never heard of a limitation or need for a workaround -- just as the article Snowhog says.

[Snowhog]

Re: 8GB RAM Kernel Panic

It's my understanding that you need the 64-bit server kernel. So, if you installed the 64-bit desktop version of Kubuntu Gutsy, the kernel isn't compiled with PAE support.

[losmurfs]

Re: 8GB RAM Kernel Panic

both 64-bit desktop and 64-bit server kernels give me the kernel panic

[dibl]

Re: 8GB RAM Kernel Panic

heh -- Snowhog is probably correct on that. FYI, my cpuid is pretty similar -- I assume your Pentium D will address 8GB just fine -- I see the PAE capability listed. Here's the output for my Core 2 Extreme:

dibl@cville:~$ cpuid
eax in eax ebx ecx edx
00000000 0000000a 756e6547 6c65746e 49656e69
00000001 000006f6 01020800 0000e3bd bfebfbff
00000002 05b0b101 005657f0 00000000 2cb43049
00000003 00000000 00000000 00000000 00000000
00000004 00000000 00000000 00000000 00000000
00000005 00000040 00000040 00000003 00000020
00000006 00000001 00000002 00000001 00000000
00000007 00000000 00000000 00000000 00000000
00000008 00000400 00000000 00000000 00000000
00000009 00000000 00000000 00000000 00000000
0000000a 07280202 00000000 00000000 00000000
80000000 80000008 00000000 00000000 00000000
80000001 00000000 00000000 00000001 20100800
80000002 65746e49 2952286c 726f4320 4d542865
80000003 43203229 20205550 20202020 58202020
80000004 30303836 20402020 33392e32 007a4847
80000005 00000000 00000000 00000000 00000000
80000006 00000000 00000000 10008040 00000000
80000007 00000000 00000000 00000000 00000000
80000008 00003024 00000000 00000000 00000000

Vendor ID: "GenuineIntel"; CPUID level 10

Intel-specific functions:
Version 000006f6:
Type 0 - Original OEM
Family 6 - Pentium Pro
Model 15 -
Extended model 0
Stepping 6
Reserved 0

Extended brand string: "Intel(R) Core(TM)2 CPU X6800 @ 2.93GHz"
CLFLUSH instruction cache line size: 8
Initial APIC ID: 1
Hyper threading siblings: 2

Feature flags bfebfbff:
FPU Floating Point Unit
VME Virtual 8086 Mode Enhancements
DE Debugging Extensions
PSE Page Size Extensions
TSC Time Stamp Counter
MSR Model Specific Registers
PAE Physical Address Extension
MCE Machine Check Exception
CX8 COMPXCHG8B Instruction
APIC On-chip Advanced Programmable Interrupt Controller present and enabled
SEP Fast System Call
MTRR Memory Type Range Registers
PGE PTE Global Flag
MCA Machine Check Architecture
CMOV Conditional Move and Compare Instructions
FGPAT Page Attribute Table
PSE-36 36-bit Page Size Extension
CLFSH CFLUSH instruction
DS Debug store
ACPI Thermal Monitor and Clock Ctrl
MMX MMX instruction set
FXSR Fast FP/MMX Streaming SIMD Extensions save/restore
SSE Streaming SIMD Extensions instruction set
SSE2 SSE2 extensions
SS Self Snoop
HT Hyper Threading
TM Thermal monitor
31 reserved

TLB and cache info:
b1: unknown TLB/cache descriptor
b0: unknown TLB/cache descriptor
05: unknown TLB/cache descriptor
f0: unknown TLB/cache descriptor
57: unknown TLB/cache descriptor
56: unknown TLB/cache descriptor
49: unknown TLB/cache descriptor
30: unknown TLB/cache descriptor
b4: unknown TLB/cache descriptor
2c: unknown TLB/cache descriptor
Processor serial: 0000-06F6-0000-0000-0000-0000


Also FYI, mine is overclocked to 3.4GHz, but as you can see the Linux utilities are mostly not detecting that correctly. The correct speed doesn't show up in KSysguard either.

[losmurfs]

Re: 8GB RAM Kernel Panic

Since I don't have an easy way (that I know of) to copy kernel panic, here is what I wrote on a piece of paper:

[ 78.917719] [<ffffff8043685a>] schedule_timeout+0x5a/0xd0
[ 78.917763] [<ffffff804360f8>] io_schedule_timeout+0x28/0x40
...
[ 78.919114] RIP [<ffffff8022c094>] dequeue_task+0x4/0x50
[ 78.919185] RSP [<ffffff805dfb78>]
[ 78.919224] CR2: 00 00 00 00 00 00 00 00
[ 78.919265] Kernel panic - not syncing: Attempted to kill the idle task!

[dibl]

Re: 8GB RAM Kernel Panic

Heh heh heh -- yep, I think you'd have to be very quick with a digital camera to catch it on screen. I'm not a kernel engineer -- I don't know what idle process was the cause of that trouble.

I dunno -- you're making me want to order another pair of 2GB G.Skill modules just to see what happens ..... :P

[losmurfs]

Re: 8GB RAM Kernel Panic

You only need 5GB to recreate the kernel panic. Anyone here have more than 4GB? (that shows up as physical ram in ksysguard?)

[dibl]

Re: 8GB RAM Kernel Panic

Here's some semi-relevant stuff found by Mr. Google:

https://bugs.launchpad.net/ubuntu/+s...22/+bug/151942

http://irclogs.ubuntu.com/2007/12/09...tu-kernel.html

http://en.wikipedia.org/wiki/Physical_Address_Extension

In that last one, I found this statement a bit scary:

The Linux kernel supports PAE starting from 2.6.[3] It has full PAE support, enabling access of up to 64 GiB of memory on 32-bit machines. A PAE-enabled Linux-kernel won't work on CPUs without PAE.

I think maybe that last sentence sheds some light -- I haven't seen a "PAE-enabled" kernel advertised as such for *buntu. And, if it won't run on non-PAE CPUs, I don't think the devs are going to put it out in the repos with no warning or notice.

[losmurfs]

Re: 8GB RAM Kernel Panic

using

make menuconfig

I could not fined where to enable or disable PAE.