From fc9fe822f7112db23e51e2be3b886f5d8f0afdb6 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 12 Dec 2012 13:50:51 -0800 Subject: thp: copy_huge_pmd(): copy huge zero page 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 [rientjes@google.com: fix comment] Signed-off-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Andi Kleen Cc: "H. Peter Anvin" Cc: Mel Gorman Signed-off-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1ee34ddb46ad..650625390f61 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -708,6 +708,18 @@ 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) @@ -785,6 +797,16 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, pte_free(dst_mm, pgtable); goto out_unlock; } + /* + * mm->page_table_lock is enough to be sure that huge zero pmd is not + * under splitting since we don't split the page itself, only pmd to + * a page table. + */ + 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); -- cgit v1.2.3