I think it would be of tremendous help if python reported the physical memory address though do not know how much work is that for you. I already said that, I wonder why memtest86+ could not find an error, I even tried other tools for that. Could --with-pydebug immediately after writing those pad bytes try to read them back, just to make sure they are readable? Theoretically one could catch the wrong bit of memory immediately.

It is random, I think CPU must be fully loaded for a long while, plus something unknown has to kick in. Maybe that has to heat up the memory modules to cause the failure. My motherboard is already 3rd but doubt it is at fault, except that the SandyBridge chip is bad by design. Was replaced few days ago with CPU cooler (was the main reason for technician to come). I take that replacing motherboard was a nice offer from Dell. I would instead think that maybe CPU is heating too much.

BIOS is weird. ACPI and PCIe ASPM are exploiting Linux kernel hotplug support and PCI developers are puzzled. I experience that SandyBridge resets e.g. its USB2.0 controller if there was a hotplug even on some of its other root ports (express card was inserted/ejected). But in overall I don't think it is a bad deal and it works. These exceptional glitches are I think a software error or BIOS error. It just wouldn't be running all the days and nights. No, it is not overheated, at least not now with the replaced cooler.

I can put in other memory module (with which I bought the laptop from Dell). Other than that, hmm ... I could take out the hard drive and attach it to some other computer, boot from Live-DVD ... the problem is I need a lot of RAM for some of my stuff and it would have to be relatively same CPU type (I compiled binaries with avx). Yes, the emerge crash definitely was another case, I could hope to get that happen on even 1GB RAM machine, sure. I just don't have a testcase for that to trigger. I tried to stitch something but no, I probably coded something not going in the right direction. If you would have the time to stitch down some test for me to execute with the garbage collector calls, it would be probably the best.