64bit + >3.6GB RAM = boom

[Kano]

Then I am sure you can live without fglrx too then I have not seen a desktop board with more than 4 memory slots. socket 775 is for desktop use.

[narf]

I have 32-bit Firefox running great with Flash, Java, Real Player, and Adobe Reader, all on my 64-bit Fedora 7 system. It's not set up that way by default, but it's not too hard to do. Everything in the 32-bit browser setup (except Sun JDK) is updated automatically with yum.

I am running the standard Fedora 7 kernel, as is. I installed my first Linux server on 0.99pl13, and I haven't had to compile a kernel in many years. I used to love mucking around with that stuff but now I don't have the time. I try to be very careful with my hardware purchases, and sometimes I have to experiment with boot params, but my machines all work fine with stock kernels.

I run multiple VMware instances simultaneously for my job, I need lots of RAM. 4 Gb barely cuts it. I have a separate drive for swap; it gets used quite a bit.

I'd also like to point out that, with Linux, there is no such thing as too much RAM, except maybe on a laptop. Buffer cache rules OK! Every machine I own is maxed out on RAM and would have more if it would fit.

There is nothing wrong, or even difficult, about running 32-bit userland apps on a 64-bit OS. I do it all the time, on Linux and Solaris. You need 32-bir libraries, but yum takes care of all that for you.

If you google for this 4 Gb issue, lots of people are having it. If you can't find good advice for your specific motherboard, make sure you have the latest BIOS, read kernel-parameters.txt carefully, and start experimenting.

[opera]

My comment was pointed at 64 bit kernels -

What makes you think I'm not running a 64-bit kernel? I am.

IF
on a 64 kernel you select IOMMU support -

this locks the AGP modules into the kernel. No module options.

I can't select IOMMU. Probably because I haven't selected EMBEDDED.. Why use either EMBEDDED or IOMMU in the first place? It's beyond me.

[MU_Engineer]

Wow... I'm starting to get a little frustrated with the whole state of 64-bit computing. I'm not sure if the problem lies in the Linux kernel or ATI's drivers, but I'm guessing the latter. Of course, it could be that I've commented out that Save64BitBar code that was causing the driver to fail to load at all.

Has anyone managed to get a 64-bit Linux machine working with 4GB of RAM?

If I try to boot with >3.6GB enabled (mem=3600M, maxmem=3600M - not sure which of these options is used), I get a hard lockup when starting the X server now. My machine reports about 3.6GB in 32-bit as well.

I saw a similar problem with my SATA controller (it would advertise 64-bit DMA but could only handle 32-bit). I imagine that this could be a similar problem, but as ATI's drivers are just blobs I'm somewhat constrained in how much I can fiddle here.

I'm excited for the day when device manufacturers have access to 64-bit + >4GB machines! At least I can say that my experience under Linux was a little less painful than my brief Windows 64-bit experiments.

I run an AMD Athlon 64 X2 4200+ (939) on an abit KN8-SLi with 4x1 GB DDR-400 and it runs Gentoo 2007.0 AMD64 just fine. The one parameter you might have to change would be to either enable or set the memory hole to "auto" or "software." If you disable this, then the BIOS will force the system address space to be mapped below 4 GB and will thus not see the full 4 GB, even with a 64-bit OS. This is only an issue becuase people are using 32-bit and 64-bit OSes on the same pieces of equipment- if they all used 64-bit OSes, then the hole would automatically be remapped by the BIOS or simply left alone for the OS to remap.

Generally the newer boards with DDR2 and 8 GB memory support fare a lot better with > 4 GB RAM than the old DDR boards that at most could take 4 GB RAM, or new notebooks with a 4 GB maximum RAM capacity. Some boards, particularly some Intel-chipset DDR and notebooks simply force the address space under 4 GB for compatibility and screw those who might want to use a 64-bit OS and a full 4 GB RAM. My notebook with a C2D U7500 and an Intel 945GM chipset explicitly does not remap the memory hole, even though the CPU supports more than 4 GB and so does the Ubuntu 7.04 AMD64 I run on it. Thus I only put 3 GB RAM in that machine as 4 GB would only give me an extra 300-500 MB usable over 3 GB.

[opera]

I run an AMD Athlon 64 X2 4200+ (939) on an abit KN8-SLi with 4x1 GB DDR-400 and it runs Gentoo 2007.0 AMD64 just fine. The one parameter you might have to change would be to either enable or set the memory hole to "auto" or "software." If you disable this, then the BIOS will force the system address space to be mapped below 4 GB and will thus not see the full 4 GB, even with a 64-bit OS. This is only an issue becuase people are using 32-bit and 64-bit OSes on the same pieces of equipment- if they all used 64-bit OSes, then the hole would automatically be remapped by the BIOS or simply left alone for the OS to remap.

Generally the newer boards with DDR2 and 8 GB memory support fare a lot better with > 4 GB RAM than the old DDR boards that at most could take 4 GB RAM, or new notebooks with a 4 GB maximum RAM capacity. Some boards, particularly some Intel-chipset DDR and notebooks simply force the address space under 4 GB for compatibility and screw those who might want to use a 64-bit OS and a full 4 GB RAM. My notebook with a C2D U7500 and an Intel 945GM chipset explicitly does not remap the memory hole, even though the CPU supports more than 4 GB and so does the Ubuntu 7.04 AMD64 I run on it. Thus I only put 3 GB RAM in that machine as 4 GB would only give me an extra 300-500 MB usable over 3 GB.

If you want to bash hardware manufacturers, I'd like to raise a note about the AGP/PCI-E systems out there. Most of them can't address 64 bits of memory, meansing, they need to allocate the AGP memory in the lower 4GB area.
This is insane, since we broke the 4GB barrier for home PC's a long time ago (not extremely common, but not really Sci-Fi neither).

The day, when peripheral devices uses 64-bit addresses, that day we won't need "holes" in the memory, or special BIOS/EFI options...

[MU_Engineer]

If you want to bash hardware manufacturers, I'd like to raise a note about the AGP/PCI-E systems out there. Most of them can't address 64 bits of memory, meansing, they need to allocate the AGP memory in the lower 4GB area.
This is insane, since we broke the 4GB barrier for home PC's a long time ago (not extremely common, but not really Sci-Fi neither).

The day, when peripheral devices uses 64-bit addresses, that day we won't need "holes" in the memory, or special BIOS/EFI options...

Well, the real reason is that the hardware manufacturers (at least in the consumer arena, servers are very different) haven't had people demand full 64-bit functionality as there hasn't been a 64-bit OS that more than a few percent of the population uses. That's due to the flop of Windows XP x(86_)64 Edition and the extremely slow uptake of Vista 64-bit. Yeah, the OSes are not the greatest and are very expensive compared to the normal 32-bit versions, but the reason there isn't wider adoption rests with the proprietary application and driver vendors not updating things for 64-bit. Oh, the loys of running a proprietary system- you're dependent upon the mercy of the companies that make your stuff and are almost always several generations behind the state-of-the-hardware curve.

[Kano]

AMD S939 can work with 4 memory modules. But when you use DS modules (SS 1 GB are very rare) then the memory speed is reduced from DDR 400 to DDR 333. This is slower until you really need lots of ram (tested with kernel compilation).

[MU_Engineer]

AMD S939 can work with 4 memory modules. But when you use DS modules (SS 1 GB are very rare) then the memory speed is reduced from DDR 400 to DDR 333. This is slower until you really need lots of ram (tested with kernel compilation).

That's only the case on 939s that are D stepping and before. The E3, E4, and E6 chips have the ability to run 4 double-sided modules at DDR-400, albeit a 2T command rate rather than a 1T command rate. The default is to run the modules at DDR-333 2T but you can go in the BIOS and set the memory to DDR-400 2T and it will work just fine. This is what I did with my E4 X2 4200+ and have had nary a problem. Might be an issue for those who use OEM machines with a crippled BIOS though.

[Kano]

Well then you are lucky, I have this one:

model name : AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
stepping : 2

[MU_Engineer]

Well then you are lucky, I have this one:

model name : AMD Athlon(tm) 64 X2 Dual Core Processor 3800+
stepping : 2

That would be an E6 chip IIRC as mine is stepping 1 and is an E4. You can run four modules of RAM at DDR-400 at 2T like I can then, as long as your BIOS allows you to adjust the memory speeds and command rate. This will be the case in most every handmade computer, but not true in almost every OEM machine. So if you have an OEM machine, you have to run them at DDR-333 I am afraid.