On Wed, Nov 14, 2012 at 03:28:15PM -0800, David Rientjes wrote:

On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:

quoted

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)
+{

This entire function duplicates other code in mm/huge_memory.c which gives 
even more incentive into breaking do_huge_pmd_wp_zero_page_fallback() into 
logical helper functions and reusing them for both page and !page.  
Duplicating all this code throughout the thp code just becomes a 
maintenance nightmare down the road.

Okay, I'll try.

quoted

+	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;

address or haddr?

haddr. I'll fix.

-- 
 Kirill A. Shutemov