Hi!
BadRAM is my kernel patch to handle broken RAM modules gracefully under Linux.
I received *many* positive replies to this patch, and several hints.
This is V3 of the patch, which I think is quite mature now, safe for inclusion
in kernel 2.2.14. Furthermore, I'll try to summarise the private discussions.
Changes:
* A minor bug on a default-added mask parameter was reported and repaired.
This bug caused a boot-time kernel freeze for an odd count of badram-parms.
* BadRAM now comes as a kernel compilation option for i386: CONFIG_BADRAM.
* Changed PG_badram bit to avoid overlap with PG_bigmem.
* (not in the kernel) I extended memtest86, an excellent RAM checker by Chris
Brady, to print the badram= boot options for my patch. Saves a lot of binary
calculations to come up with the patterns! Memtest86 can boot from LILO.
* (not in the kernel) I had to patch LILO 0.21 to avoid cutting off command
lines after the 78th character, while kernel accepts 255!
Todo:
* Use lmbench to prove that BadRAM has *no* performance impact at all.
* Incorporate non-i386 support as soon as owners of such machines help out.
* See if a 15M-16M hole can be ignored/handler/... with this patch.
* Seek integration with either 2.3.x or 2.4.0.
Discussions:
* Build a RAM checker into the kernel. Not done, would be hard to cover all.
The boot alternative for memtest86 from LILO seems to be the best solution.
* Concentrate on the matter of statically damaged RAMs instead of manufactured
mistakes. I think BadRAM can do both.
* Environmental. Fall-out in a mature chip baking process is 10-60%, exp 50-95%
RAM chips may be different, they incorporate some hardware redundancy.
Either way, chip production requires loads of toxic and energy. Every penny
saved is worth a dime (to me).
* Laptops sometimes have RAM soldered in. If it fails... throw away your
laptop or apply BadRAM. Quite a money-saver there!
References:
* BadRAM home page http://home.zonnet.nl/vanrein/badram
* Memtest86 home page http://reality.sgi.com/cbrady_denver/memtest86
* BadRAM patch for 2.2.14 http://home.zonnet.nl/vanrein/badram/badram-patch.V3
* LILO 0.21 micropatch http://home.zonnet.nl/vanrein/badram/lilo-0.21-patch
* Memtest86 2.2 patch http://home.zonnet.nl/vanrein/badram/memtest86-2.2-patch
Acknowledgements:
* Val Henson for digging up figures on drop-out of chip manufacture.
* Jeff Hildebrand for lots of testing remarks and the odd-parms bug report.
* Uwe Klein for remarks on PG_bigmem and the odd-parms bug report.
* Rogier Wolff for pointing out that modern RAMs have on-chip redundancy.
* Peter F. Curran for pointing out the 15M-16M hole thing.
* Dennis Vierkant for helping me to testing material: Broken DIMMs.
* Luuk van der Duim and many others for keeping me enthousiastic about BadRAM.
* Y'all for Linux. It's more stable to hack than using Word under other OS's!
Enjoy,
-Rick.
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