On Sat, Feb 20, 2016 at 12:39:42PM +1100, Paul Mackerras wrote: > It seems there's something wrong with our transparent hugepage > implementation on POWER server processors as of v4.5-rc4. I have seen > the email thread on "[BUG] random kernel crashes after THP rework on > s390 (maybe also on PowerPC and ARM)", but this doesn't seem exactly > the same as that (though it may of course be related). > > I have been testing v4.5-rc4 with Aneesh's patch "powerpc/mm/hash: > Clear the invalid slot information correctly" on top, on a KVM guest > with 160 vcpus (threads=8) and 32GB of memory backed by 16MB large > pages, running on a POWER8 machine running a 4.4.1 host kernel (20 > cores * 8 threads, 128GB of RAM). The guest kernel is compiled with > THP enabled and set to "always" (i.e. not "madvise"). > > On this setup, when doing something like a large kernel compile, I see > random segfaults happening (in gcc, cc1, sh, etc.). I also see bursts > of messages like this on the host console: > > [50957.570859] Harmless Hypervisor Maintenance interrupt [Recovered] > [50957.570864] Error detail: Processor Recovery done > [50957.570869] HMER: 2040000000000000 When I use a merge of v4.5-rc4 with the fixes branch from the powerpc tree, I don't see these messages any more, presumably due to "powerpc/mm: Fix Multi hit ERAT cause by recent THP update". With my patch, I still see that it is finding HPTEs to invalidate, but without my patch, even though it is presumably leaving HPTEs around, I don't see any errors (such as random segfaults) occurring. Paul. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>