Thread (34 messages) 34 messages, 5 authors, 2012-10-26
STALE4993d
Revisions (6)
  1. rfc [diff vs current]
  2. v2 [diff vs current]
  3. v3 [diff vs current]
  4. v4 current
  5. v5 [diff vs current]
  6. v6 [diff vs current]

[PATCH v4 03/10] thp: copy_huge_pmd(): copy huge zero page

From: Kirill A. Shutemov <hidden>
Date: 2012-10-15 06:02:40
Also in: lkml
Subsystem: memory management, memory management - thp (transparent huge page), the rest · Maintainers: Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds

From: "Kirill A. Shutemov" <redacted>

It's easy to copy huge zero page. Just set destination pmd to huge zero
page.

It's safe to copy huge zero page since we have none yet :-p

Signed-off-by: Kirill A. Shutemov <redacted>
---
 mm/huge_memory.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 680c27f..9f5e5cb 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -700,6 +700,18 @@ static inline struct page *alloc_hugepage(int defrag)
 }
 #endif
 
+static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
+		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd)
+{
+	pmd_t entry;
+	entry = pfn_pmd(huge_zero_pfn, vma->vm_page_prot);
+	entry = pmd_wrprotect(entry);
+	entry = pmd_mkhuge(entry);
+	set_pmd_at(mm, haddr, pmd, entry);
+	pgtable_trans_huge_deposit(mm, pgtable);
+	mm->nr_ptes++;
+}
+
 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			       unsigned long address, pmd_t *pmd,
 			       unsigned int flags)
@@ -777,6 +789,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		pte_free(dst_mm, pgtable);
 		goto out_unlock;
 	}
+	if (is_huge_zero_pmd(pmd)) {
+		set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd);
+		ret = 0;
+		goto out_unlock;
+	}
 	if (unlikely(pmd_trans_splitting(pmd))) {
 		/* split huge page running from under us */
 		spin_unlock(&src_mm->page_table_lock);
-- 
1.7.7.6

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