# Kernel maximum memory [Closed: worked-around]

## TJNII

I can't boot Linux on a system with >256G of ram.  What is the maximum amount of memory currently supported by the kernel?

More importantly, what site can I go to to find out?  I don't see it on kernel.org, and google isn't helping.  Well, not helping in a fashion I find authoritative, at least.

Thanks.Last edited by TJNII on Mon Oct 25, 2010 11:39 pm; edited 1 time in total

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## sebaro

http://widefox.pbworks.com/Memory

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## Hu

More than 256 Gigabytes of RAM?  Is that correct?  On what architecture are you trying to do this?  What error do you receive when the kernel panics?

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## TJNII

Yes, >256G of ram.  That is correct.  That is what I currently believe the problem is.  I can boot my kernel on a 8 socket ia64 system with 32 gigs of ram fine.  If I try and boot it on a 8 socket system with 512 gigs of ram the system MCAs immediately after the kernel uncompresses.  The kernel itself doesn't panic or print anything, it just crashes.  I can get it to boot on a 4 socket system with 256G of ram, but not any higher.

My current working kernel is 2.6.31, which is why I was curious about an authoritative source.   I tried downloading the newest 2.6.36 kernel and booting that, but it had other problems and wouldn't boot properly on my known working systems, so I didn't try it on the new one.  I haven't tried the 2.6.34 or 2.6.35 kernels yet.

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## Etal

Since you have a pretty "unusual" system that probably not a lot of people on here have, have you considered asking on the Linux Kernel mailing lists? (linux-kernel and linux-ia64, I'd guess)

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## eccerr0r

Curiousity, what system is this (hardware/chipset) and what processor?

Have any MCA MSR data handy?  Not sure if the MCA handler will dump any of this data out, never had my ia64 box crash so bad it would MCA.

Authoritative source would be your vendor of course... This can't be a very old machine (my old ia64 machine tops out at like 16G (8 slots of 2GB) so this should be under warranty  :Smile: 

Even some old IA64 chips, the CPU can work with I think 1PB physical RAM ('till it runs out of tag bits), so likely the MCA is being triggered from the chipset.

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## TJNII

I really don't want to give too much information as this topic is straying into NDA territory here.

It is new.  Really new.  The hardware is operating properly, I tested it.  The kernel is passing a bad address to the hardware, don't ask me how I know that.  The MCA is caused by software and recoverable, but since the kernel is still in early boot it doesn't.  Linux isn't officially supported on this system, so I won't be contacting support.

I really just want to know if kernel.org or the Documentation states what the maximum is on a per-kernel release basis.  It is looking like grepping the changelog is my best bet.

And no, I haven't pinged the kernel lists yet.  I want to do some more footwork first, especially around the 2.6.36 bugs I saw.

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## eccerr0r

Yes LKML would be a place to start...  I'm sure there's really no arbitrary limit.

I'm sure if you contact Intel they would want to know.  There are some who IRC on #ia64 on oftc ... there's a Linux-ia64-centric guy there that works for Intel, who I'm sure would be interested.

(dang, now you've got me really curious what you're working on ... and since I have my own ia64-NDAs to deal with, you're killing me... since it sounds like one of the newer QPI 9300-series Itaniums... or "even newer"... )

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## Hu

 *TJNII wrote:*   

> I really don't want to give too much information as this topic is straying into NDA territory here.

 Although Linux may not be officially supported on the hardware, it might be worth contacting your vendor to see if they will arrange to bring into the NDA someone from Intel (or the kernel developers or ideally someone who works at Intel and on the kernel) who would have the necessary technical expertise to resolve the issue.  Depending on why you have the hardware and what they hope to obtain from the NDA, they might be willing to do so, especially if it offers the chance to get Linux working on their hardware at no cost beyond having their lawyers handle the NDA changes.

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## eccerr0r

from the posting it sounds too much like he's working for a hardware developer ... They are the few who have tools to get addresses off the bus and actually know they're wrong (LA... JTAG?)...  though I'm surprised Gentoo was chosen over SuSE or something... 

Anyway, Go ia64 (reasons unden NDA  :Smile: )!

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## chithanh

Does the kernel still crash if you limit maximum used memory with the mem=... kernel option?

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## TJNII

 *chithanh wrote:*   

> Does the kernel still crash if you limit maximum used memory with the mem=... kernel option?

 

No.  If I pass mem=256G it still crashes, but mem=128G works.  I tried this with the 2.6.35.7 kernel.

 *ecerr0r wrote:*   

> I'm surprised Gentoo was chosen over SuSE or something...

 

Well, the kernel is vanilla with the unionfs patchset so the distro doesn't really come into to play much there.  Otherwise, well, I like Gentoo.

So, as this is an install I use for my own testing / tinkering, I'm going to call this resolved.  As much as I would like to have all the memory available, I think I can survive with only 128 gigs of ram.  I've decided not to contact LKML. The 2.6.36 issues I saw were either caused by human error or the unionfs patches.  As for my root issue, I'm afraid I'd have to publicly divulge too much information to get it fixed and I'm afraid of getting fired / sued.  So thanks for the tips, I'm calling it a day.

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## eccerr0r

I still think Intel would be interested in the problem, if you have a chance, ask aegl (Tony Luck) on irc.oftc.net, he an Intel guy who's also on LKML quite a bit as he seems to gatekeep all the ia64 Linux kernel commits.

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## TJNII

Yea, but there's more to the story than I'm letting on.  (Which I'm sure you've already guessed, Mr. Perceptive.)  Rumor has it there are some guys working on getting Linux on this thing in a official capacity, I may go pester them.

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