[PATCH v5 07/11] thp: implement splitting pmd for huge zero page

Kirill A. Shutemov
2012-11-07T15:00:56Z

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

We can't split huge zero page itself (and it's bug if we try), but we
can split the pmd which points to it.

On splitting the pmd we create a table with all ptes set to normal zero
page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
mm/huge_memory.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
1 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 90e651c..f36bc7d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1611,6 +1611,7 @@ int split_huge_page(struct page *page)
struct anon_vma *anon_vma;
int ret = 1;

+ BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
BUG_ON(!PageAnon(page));
anon_vma = page_lock_anon_vma(page);
if (!anon_vma)
@@ -2509,23 +2510,63 @@ 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)
+{
+ pgtable_t pgtable;
+ pmd_t _pmd;
+ int i;
+
+ pmdp_clear_flush(vma, haddr, pmd);
+ /* leave pmd empty until pte is filled */
+
+ pgtable = get_pmd_huge_pte(vma->vm_mm);
+ pmd_populate(vma->vm_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(vma->vm_mm, haddr, pte, entry);
+ pte_unmap(pte);
+ }
+ smp_wmb(); /* make pte visible before pmd */
+ pmd_populate(vma->vm_mm, pmd, pgtable);
+}
+
void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmd)
{
struct page *page;
+ struct mm_struct *mm = vma->vm_mm;
unsigned long haddr = address & HPAGE_PMD_MASK;
+ unsigned long mmun_start; /* For mmu_notifiers */
+ unsigned long mmun_end; /* For mmu_notifiers */

BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);

- spin_lock(&vma->vm_mm->page_table_lock);
+ mmun_start = haddr;
+ mmun_end = address + HPAGE_PMD_SIZE;
+ mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+ spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_trans_huge(*pmd))) {
- spin_unlock(&vma->vm_mm->page_table_lock);
+ spin_unlock(&mm->page_table_lock);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+ return;
+ }
+ if (is_huge_zero_pmd(*pmd)) {
+ __split_huge_zero_page_pmd(vma, haddr, pmd);
+ spin_unlock(&mm->page_table_lock);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
return;
}
page = pmd_page(*pmd);
VM_BUG_ON(!page_count(page));
get_page(page);
- spin_unlock(&vma->vm_mm->page_table_lock);
+ spin_unlock(&mm->page_table_lock);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);

split_huge_page(page);

--
1.7.7.6