On Fri, Feb 05, 2016 at 11:41:40PM +0530, Aneesh Kumar K.V wrote: > With ppc64 we use the deposted pgtable_t to store the hash pte slot > information. We should not withdraw the deposited pgtable_t without > marking the pmd none. This ensure that low level hash fault handling > will skip this huge pte and we will handle them at upper levels. We > do take page table lock there and we can serialize against a parallel > THP split there. Hence mark the pte none (ie, remove __PAGE_USER) before > splitting the huge pmd. > > Also make sure we wait for irq disable section in other cpus to finish > before flipping a huge pte entry with a regular pmd entry. Code paths > like find_linux_pte_or_hugepte depend on irq disable to get > a stable pte_t pointer. A parallel thp split need to make sure we > don't convert a pmd pte to a regular pmd entry without waiting for the > irq disable section to finish. > > Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
Cc list is too short. At least akpm@ and linux-mm@ should be there. Probably numa balancing folks. Have you tested it with CONFIG_NUMA_BALANCING disabled? I would expect some additional changes in this area would be required. pmd_protnone() is always zero without numa balancing compiled in and therefore I don't see where we will get this serialization agians ptl on fault side. > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 4 ++++ > arch/powerpc/mm/pgtable_64.c | 36 > +++++++++++++++++++++++++++- > include/asm-generic/pgtable.h | 8 +++++++ > mm/huge_memory.c | 1 + > 4 files changed, 48 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 8d1c41d28318..0415856941e0 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -281,6 +281,10 @@ extern pgtable_t pgtable_trans_huge_withdraw(struct > mm_struct *mm, pmd_t *pmdp); > extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long > address, > pmd_t *pmdp); > > +#define __HAVE_ARCH_PMDP_HUGE_SPLITTING_FLUSH > +extern void pmdp_huge_splitting_flush(struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmdp); I don't really like the name, but cannot think of anything better. > + > #define pmd_move_must_withdraw pmd_move_must_withdraw > struct spinlock; > static inline int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl, > diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c > index 3124a20d0fab..d80a23a92f95 100644 > --- a/arch/powerpc/mm/pgtable_64.c > +++ b/arch/powerpc/mm/pgtable_64.c > @@ -646,6 +646,31 @@ pgtable_t pgtable_trans_huge_withdraw(struct mm_struct > *mm, pmd_t *pmdp) > return pgtable; > } > > +void pmdp_huge_splitting_flush(struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmdp) > +{ > + VM_BUG_ON(address & ~HPAGE_PMD_MASK); > + > +#ifdef CONFIG_DEBUG_VM > + BUG_ON(REGION_ID(address) != USER_REGION_ID); > +#endif > + /* > + * We can't mark the pmd none here, because that will cause a race > + * against exit_mmap. We need to continue mark pmd TRANS HUGE, while > + * we spilt, but at the same time we wan't rest of the ppc64 code > + * not to insert hash pte on this, because we will be modifying > + * the deposited pgtable in the caller of this function. Hence > + * clear the _PAGE_USER so that we move the fault handling to > + * higher level function and that will serialize against ptl. > + * We need to flush existing hash pte entries here even though, > + * the translation is still valid, because we will withdraw > + * pgtable_t after this. > + */ > + pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_USER, 0); > + return; > +} > + > + > /* > * set a new huge pmd. We should not be called for updating > * an existing pmd entry. That should go via pmd_hugepage_update. > @@ -663,10 +688,19 @@ void set_pmd_at(struct mm_struct *mm, unsigned long > addr, > return set_pte_at(mm, addr, pmdp_ptep(pmdp), pmd_pte(pmd)); > } > > +/* > + * We use this to invalidate a pmdp entry before switching from a > + * hugepte to regular pmd entry. > + */ > void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmdp) > { > - pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0); > + pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); > + /* > + * This ensures that generic code that rely on IRQ disabling > + * to prevent a parallel THP split work as expected. > + */ > + kick_all_cpus_sync(); > } > > /* > diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h > index 0b3c0d39ef75..388065c79795 100644 > --- a/include/asm-generic/pgtable.h > +++ b/include/asm-generic/pgtable.h > @@ -239,6 +239,14 @@ extern void pmdp_invalidate(struct vm_area_struct *vma, > unsigned long address, > pmd_t *pmdp); > #endif > > +#ifndef __HAVE_ARCH_PMDP_HUGE_SPLITTING_FLUSH > +static inline void pmdp_huge_splitting_flush(struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmdp) > +{ > + return; > +} > +#endif > + > #ifndef __HAVE_ARCH_PTE_SAME > static inline int pte_same(pte_t pte_a, pte_t pte_b) > { > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 36c070167b71..b52d16a86e91 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2860,6 +2860,7 @@ static void __split_huge_pmd_locked(struct > vm_area_struct *vma, pmd_t *pmd, > young = pmd_young(*pmd); > dirty = pmd_dirty(*pmd); > > + pmdp_huge_splitting_flush(vma, haddr, pmd); > pgtable = pgtable_trans_huge_withdraw(mm, pmd); > pmd_populate(mm, &_pmd, pgtable); > > -- > 2.5.0 > -- Kirill A. Shutemov _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev