On 01/22, Hugh Dickins wrote: > > On Wed, 22 Jan 2014, Oleg Nesterov wrote: > > > hugepage_madvise() checks "mm->def_flags & VM_NOHUGEPAGE" but > > this can be never true, currently mm->def_flags can only have > > VM_LOCKED. > > But line 1087 of arch/s390/mm/pgtable.c says > mm->def_flags |= VM_NOHUGEPAGE; > from 3eabaee998c787e7e1565574821652548f7fc003 > "KVM: s390: allow sie enablement for multi-threaded programs".
Argh. Thanks Hugh! Another case when I forgot about /bin/grep. So the patch is wrong, at least the changelog is certainly is. I am stupid. But, perhaps, this all still can work? Looks like, s390 already implements PR_SET_THP_DISABLE using the same idea, it would be nice to avoid another hack. Gerald, any chance we can revert 8e72033f2a489 "thp: make MADV_HUGEPAGE check for mm->def_flags" ? The changelog says "In order to also prevent MADV_HUGEPAGE on such an mm", is it really important? I mean, if the application calls madvise(MADV_HUGEPAGE) it should probably know what it does and, this can be useful after if PR_SET_THP_DISABLE or KVM_S390_ENABLE_SIE. Of course I do not understand this code, perhaps MADV_HUGEPAGE is simply impossible. Another question, can't fork/exec preserve VM_NOHUGEPAGE in ->def_flags? This is what PR_SET_THP_DISABLE wants. I'll send you mbox with the previous discussion privately. Thanks, Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
