thp: implement split_huge_pmd()

[cascardo/linux.git] / mm / huge_memory.c

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1588f68..22ab365 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2666,6 +2666,130 @@ static int khugepaged(void *none)
        return 0;
 }
 
+static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
+               unsigned long haddr, pmd_t *pmd)
+{
+       struct mm_struct *mm = vma->vm_mm;
+       pgtable_t pgtable;
+       pmd_t _pmd;
+       int i;
+
+       /* leave pmd empty until pte is filled */
+       pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+
+       pgtable = pgtable_trans_huge_withdraw(mm, pmd);
+       pmd_populate(mm, &_pmd, pgtable);
+
+       for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+               pte_t *pte, entry;
+               entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
+               entry = pte_mkspecial(entry);
+               pte = pte_offset_map(&_pmd, haddr);
+               VM_BUG_ON(!pte_none(*pte));
+               set_pte_at(mm, haddr, pte, entry);
+               pte_unmap(pte);
+       }
+       smp_wmb(); /* make pte visible before pmd */
+       pmd_populate(mm, pmd, pgtable);
+       put_huge_zero_page();
+}
+
+static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
+               unsigned long haddr)
+{
+       struct mm_struct *mm = vma->vm_mm;
+       struct page *page;
+       pgtable_t pgtable;
+       pmd_t _pmd;
+       bool young, write;
+       int i;
+
+       VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
+       VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
+       VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
+       VM_BUG_ON(!pmd_trans_huge(*pmd));
+
+       count_vm_event(THP_SPLIT_PMD);
+
+       if (vma_is_dax(vma)) {
+               pmd_t _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+               if (is_huge_zero_pmd(_pmd))
+                       put_huge_zero_page();
+               return;
+       } else if (is_huge_zero_pmd(*pmd)) {
+               return __split_huge_zero_page_pmd(vma, haddr, pmd);
+       }
+
+       page = pmd_page(*pmd);
+       VM_BUG_ON_PAGE(!page_count(page), page);
+       atomic_add(HPAGE_PMD_NR - 1, &page->_count);
+       write = pmd_write(*pmd);
+       young = pmd_young(*pmd);
+
+       /* leave pmd empty until pte is filled */
+       pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+
+       pgtable = pgtable_trans_huge_withdraw(mm, pmd);
+       pmd_populate(mm, &_pmd, pgtable);
+
+       for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+               pte_t entry, *pte;
+               /*
+                * Note that NUMA hinting access restrictions are not
+                * transferred to avoid any possibility of altering
+                * permissions across VMAs.
+                */
+               entry = mk_pte(page + i, vma->vm_page_prot);
+               entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+               if (!write)
+                       entry = pte_wrprotect(entry);
+               if (!young)
+                       entry = pte_mkold(entry);
+               pte = pte_offset_map(&_pmd, haddr);
+               BUG_ON(!pte_none(*pte));
+               set_pte_at(mm, haddr, pte, entry);
+               atomic_inc(&page[i]._mapcount);
+               pte_unmap(pte);
+       }
+
+       /*
+        * Set PG_double_map before dropping compound_mapcount to avoid
+        * false-negative page_mapped().
+        */
+       if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
+               for (i = 0; i < HPAGE_PMD_NR; i++)
+                       atomic_inc(&page[i]._mapcount);
+       }
+
+       if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
+               /* Last compound_mapcount is gone. */
+               __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
+               if (TestClearPageDoubleMap(page)) {
+                       /* No need in mapcount reference anymore */
+                       for (i = 0; i < HPAGE_PMD_NR; i++)
+                               atomic_dec(&page[i]._mapcount);
+               }
+       }
+
+       smp_wmb(); /* make pte visible before pmd */
+       pmd_populate(mm, pmd, pgtable);
+}
+
+void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+               unsigned long address)
+{
+       spinlock_t *ptl;
+       struct mm_struct *mm = vma->vm_mm;
+       unsigned long haddr = address & HPAGE_PMD_MASK;
+
+       mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
+       ptl = pmd_lock(mm, pmd);
+       if (likely(pmd_trans_huge(*pmd)))
+               __split_huge_pmd_locked(vma, pmd, haddr);
+       spin_unlock(ptl);
+       mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
+}
+
 static void split_huge_pmd_address(struct vm_area_struct *vma,
                                    unsigned long address)
 {