Paul Mackerras <paulus@xxxxxxxxxx> writes: > 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. > Yes that patch should fix that. With thp, we use the deposited page table to store hash pte slot information. On splitting, we were doing a withdraw of deposited table, without doing the required hash pte flush. This fix is to call pmdp_huge_split_prepare, which does the required flush and also clear the _PAGE_USER. Clearning _PAGE_USER ensure that we don't be inserting any other hash pte entries w.r.t to this THP. -aneesh -- 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>