On Wed, 22 Jun 2011 11:00:34 -0700 Andrew Morton wrote: > On Wed, 22 Jun 2011 13:18:51 +0200 Stefan Assmann <sassmann@xxxxxxxxx> wrote: > > > Following the RFC for the BadRAM feature here's the updated version with > > spelling fixes, thanks go to Randy Dunlap. Also the code is now less verbose, > > as requested by Andi Kleen. > > v2 with even more spelling fixes suggested by Randy. > > Patches are against vanilla 2.6.39. > > > > The idea is to allow the user to specify RAM addresses that shouldn't be > > touched by the OS, because they are broken in some way. Not all machines have > > hardware support for hwpoison, ECC RAM, etc, so here's a solution that allows to > > use bitmasks to mask address patterns with the new "badram" kernel command line > > parameter. > > Memtest86 has an option to generate these patterns since v2.3 so the only thing > > for the user to do should be: > > - run Memtest86 > > - note down the pattern > > - add badram=<pattern> to the kernel command line > > > > The concerning pages are then marked with the hwpoison flag and thus won't be > > used by the memory managment system. > > The google kernel has a similar capability. I asked Nancy to comment > on these patches and she said: > > : One, the bad addresses are passed via the kernel command line, which > : has a limited length. It's okay if the addresses can be fit into a > : pattern, but that's not necessarily the case in the google kernel. And > : even with patterns, the limit on the command line length limits the > : number of patterns that user can specify. Instead we use lilo to pass > : a file containing the bad pages in e820 format to the kernel. > : > : Second, the BadRAM patch expands the address patterns from the command > : line into individual entries in the kernel's e820 table. The e820 > : table is a fixed buffer that supports a very small, hard coded number > : of entries (128). We require a much larger number of entries (on > : the order of a few thousand), so much of the google kernel patch deals > : with expanding the e820 table. Also, with the BadRAM patch, entries > : that don't fit in the table are silently dropped and this isn't > : appropriate for us. > : > : Another caveat of mapping out too much bad memory in general. If too > : much memory is removed from low memory, a system may not boot. We > : solve this by generating good maps. Our userspace tools do not map out > : memory below a certain limit, and it verifies against a system's iomap > : that only addresses from memory is mapped out. > > I have a couple of thoughts here: > > - If this patchset is merged and a major user such as google is > unable to use it and has to continue to carry a separate patch then > that's a regrettable situation for the upstream kernel. > > - Google's is, afaik, the largest use case we know of: zillions of > machines for a number of years. And this real-world experience tells > us that the badram patchset has shortcomings. Shortcomings which we > can expect other users to experience. > > So. What are your thoughts on these issues? Good comments, so where is google's patch submittal? --- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code *** -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>