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Subject[PATCH 3/4] Hugetlb: Reorganize hugetlb_fault to prepare for COW
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Hugetlb: Reorganize hugetlb_fault to prepare for COW

This patch splits the "no_page()" type activity into its own function,
hugetlb_no_page(). hugetlb_fault() becomes the entry point for hugetlb faults
and delegates to the appropriate handler depending on the type of fault. Right
now we still have only hugetlb_no_page() but a later patch introduces a COW
fault.

Original post by David Gibson <david@gibson.dropbear.id.au>

Version 2: Wed 9 Nov 2005
Broken out into a separate patch

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Adam Litke <agl@us.ibm.com>
---
hugetlb.c | 34 +++++++++++++++++++++++++---------
1 files changed, 25 insertions(+), 9 deletions(-)
diff -upN reference/mm/hugetlb.c current/mm/hugetlb.c
--- reference/mm/hugetlb.c
+++ current/mm/hugetlb.c
@@ -370,20 +370,15 @@ out:
return page;
}

-int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
- unsigned long address, int write_access)
+int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, pte_t *ptep)
{
int ret = VM_FAULT_SIGBUS;
unsigned long idx;
unsigned long size;
- pte_t *pte;
struct page *page;
struct address_space *mapping;

- pte = huge_pte_alloc(mm, address);
- if (!pte)
- goto out;
-
mapping = vma->vm_file->f_mapping;
idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
@@ -402,11 +397,11 @@ int hugetlb_fault(struct mm_struct *mm,
goto backout;

ret = VM_FAULT_MINOR;
- if (!pte_none(*pte))
+ if (!pte_none(*ptep))
goto backout;

add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
- set_huge_pte_at(mm, address, pte, make_huge_pte(vma, page));
+ set_huge_pte_at(mm, address, ptep, make_huge_pte(vma, page));
spin_unlock(&mm->page_table_lock);
unlock_page(page);
out:
@@ -420,6 +415,27 @@ backout:
goto out;
}

+int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long address, int write_access)
+{
+ pte_t *ptep;
+ pte_t entry;
+
+ ptep = huge_pte_alloc(mm, address);
+ if (!ptep)
+ return VM_FAULT_OOM;
+
+ entry = *ptep;
+ if (pte_none(entry))
+ return hugetlb_no_page(mm, vma, address, ptep);
+
+ /*
+ * We could get here if another thread instantiated the pte
+ * before the test above.
+ */
+ return VM_FAULT_MINOR;
+}
+
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)
--
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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