hugepage: support ZERO_PAGE() (4b2e38ad) · Commits · 戴 / test

Presently hugepage doesn't use zero page at all because zero page is only used for coredumping and hugepage can't core dump. However we have now implemented hugepage coredumping. Therefore we should implement the zero page of hugepage. Implementation note: o Why do we only check VM_SHARED for zero page? normal page checked as .. static inline int use_zero_page(struct vm_area_struct *vma) { if (vma->vm_flags & (VM_LOCKED | VM_SHARED)) return 0; return !vma->vm_ops || !vma->vm_ops->fault; } First, hugepages are never mlock()ed. We aren't concerned with VM_LOCKED. Second, hugetlbfs is a pseudo filesystem, not a real filesystem and it doesn't have any file backing. Thus ops->fault checking is meaningless. o Why don't we use zero page if !pte. !pte indicate {pud, pmd} doesn't exist or some error happened. So we shouldn't return zero page if any error occurred. Signed-off-by:

KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Adam Litke <agl@us.ibm.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Kawai Hidehiro <hidehiro.kawai.ez@hitachi.com> Cc: Mel Gorman <mel@skynet.ie> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

+19 −3

Original line number	Diff line number	Diff line
		@@ -2071,6 +2071,14 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
		return NULL;
		}

		static int huge_zeropage_ok(pte_t *ptep, int write, int shared)
		{
		if (!ptep \|\| write \|\| shared)
		return 0;
		else
		return huge_pte_none(huge_ptep_get(ptep));
		}

		int follow_hugetlb_page(struct mm_struct mm, struct vm_area_struct vma,
		struct page pages, struct vm_area_struct vmas,
		unsigned long position, int length, int i,
		@@ -2080,6 +2088,8 @@ int follow_hugetlb_page(struct mm_struct mm, struct vm_area_struct vma,
		unsigned long vaddr = *position;
		int remainder = *length;
		struct hstate *h = hstate_vma(vma);
		int zeropage_ok = 0;
		int shared = vma->vm_flags & VM_SHARED;

		spin_lock(&mm->page_table_lock);
		while (vaddr < vma->vm_end && remainder) {
		@@ -2092,8 +2102,11 @@ int follow_hugetlb_page(struct mm_struct mm, struct vm_area_struct vma,
		* first, for the page indexing below to work.
		*/
		pte = huge_pte_offset(mm, vaddr & huge_page_mask(h));
		if (huge_zeropage_ok(pte, write, shared))
		zeropage_ok = 1;

		if (!pte \|\| huge_pte_none(huge_ptep_get(pte)) \|\|
		if (!pte \|\|
		(huge_pte_none(huge_ptep_get(pte)) && !zeropage_ok) \|\|
		(write && !pte_write(huge_ptep_get(pte)))) {
		int ret;

		@@ -2113,8 +2126,11 @@ int follow_hugetlb_page(struct mm_struct mm, struct vm_area_struct vma,
		page = pte_page(huge_ptep_get(pte));
		same_page:
		if (pages) {
		get_page(page);
		if (zeropage_ok)
		pages[i] = ZERO_PAGE(0);
		else
		pages[i] = page + pfn_offset;
		get_page(pages[i]);
		}

		if (vmas)

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