Problems with AMD64 and 8 GB RAM?

[Scott Long]

Greg 'groggy' Lehey wrote:
> I've recently acquired an AMD64 box (dual Opteron 242, SiS Master at -FAR
> motherboard
> (http://www.msi.com.tw/program/products/server/svr/pro_svr_detail.php?UID=484).
> See below for more details).  I find it very unstable running with 8
> GB memory, though 4 GB are not a problem.  At first I thought it was
> the onboard peripherals, but after disabling them it still persisted.
> 
> What's unstable?  I only once got it through the boot process.
> Running a 5.3-RELEASE i386 kernel it panics, though I haven't
> investigated the panic (yet), since I'm not interested in the i386
> kernel.  The amd64 5.4-PRERELEASE kernel just hangs/freezes.  When the
> peripherals are enabled, it's after probing the onboard NIC (bge) and
> before probing SATA (no drives present).  I've done a verbose boot, of
> course, but no additional information is present.  The NIC is
> recognized, and that's all.
> 

> Without the peripherals, but with a 3Com 3c905 PCI NIC, it continues
> beyond this point, but doesn't enable the NIC.  I don't have dmesg
> output for these attempts, so I can't produce the exact message, and I
> suspect it's not important.  It continues until trying to mount NFS
> file systems, where it hangs for obvious reasons.  Pressing ^C causes
> the system to either panic (and be unable to dump because I don't have
> that much swap) or just hang.
> 
> None of these problems occur when I use 4 GB memory.  About the only
> strangeness, which seems to come from the BIOS, is that it recognizes
> only 3.5 GB.  If I put all DIMMS in, it recognizes the full 8 GB
> memory.
> 
> I realize that this isn't enough to diagnose the problem.  The reason
> for this message now is to ask:
> 
> 1.  Has anybody else seen this problem?
> 2.  Has anybody else used this hardware configuration and *not* seen
>     this problem?
> 3.  Where should I look next?
> 
> I'm attaching the (non-verbose) dmesg from a successful boot.
> 
> Greg
> --
> See complete headers for address and phone numbers.
> 

5.3-RELEASE has a lot of problems with >4GB due to busdma issues.  Those
should no longer be an issue in RELENG_5, including 5.4-PRE.  You'll
need to dig in and provide some more details, I guess.  I have an HDAMA
dual Opteron system that behaves fine now with 8GB of RAM, so your
problem might lie with particular hardware and/or drivers.

Scott