On Wed, Feb 25, 2015 at 01:31:40PM -0800, Andrew Morton wrote: > On Wed, 25 Feb 2015 22:47:43 +0200 "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote: > > > > > If not, I can prepare a patchset which only adds missing > > > > __PAGETABLE_PUD_FOLDED and __PAGETABLE_PMD_FOLDED. > > > > > > Something simple would be preferred, but I don't know how much simpler > > > the above would be? > > > > Not much simplier: __PAGETABLE_PMD_FOLDED is missing in frv, m32r, m68k, > > mn10300, parisc and s390. > > I don't really know what's going on here. Let's rewind a bit, please. > What is the bug, what causes it, which commit caused it and why the > heck does it require a massive patchset to fix 4.0? PMD accounting happens in __pmd_alloc() and free_pmd_range(). PMD accounting only makes sense on architectures with 3 or more page tables levels. We use __PAGETABLE_PMD_FOLDED to check whether the PMD page table level exists. Unfortunately, some architectures don't use <asm-generic/pgtable-nopmd.h> to indicate that PMD level doesn't exists and fold it in a custom way. Some of them don't define __PAGETABLE_PMD_FOLDED as pgtable-nopmd.h does. Missing __PAGETABLE_PMD_FOLDED causes undeflow of mm->nr_pmds: __pmd_alloc() is never called, but we decrement mm->nr_pmds in free_pmd_range(). These architecures need to be fixed to define __PAGETABLE_PMD_FOLDED too. I can do in one patch if you want. Or split per-arch. After that CONFIG_PGTABLE_LEVELS patchset will require rebasing. -- Kirill A. Shutemov -- 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>